A year ago, Lionel Messi set out his terms for staying at Barcelona. "I want to be at Barcelona for as long as possible. This is my home," he told the Catalan newspaper Sport. "But I don't want to have a long-term contract and to only be here because of it. I need to see that there's a winning team because I want to keep winning things at this club.

"For me, money or a clause don't mean anything. I don't have any intention of going anywhere but I want to keep competing and winning."

Twelve months later, Messi was refusing to train, insisting that his 20-year relationship with Barca was over, and trying to force a move to Manchester City.

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That Messi, one-club man, captain and icon, would seek to leave Barcelona like this -- notifying them in a now-infamous burofax that, as far as he was concerned, he had already gone -- should have been unthinkable. And yet this was no spur-of-the-moment decision. We should have seen it coming.

Messi had not been happy at Barcelona -- with the president, the board or management -- for a long time. He admitted as much in the interview that brought a temporary end to the crisis this summer: "I've been telling [president Josep Maria Bartomeu] that I wanted to leave all year." Known for being a reluctant public figure, Messi speaks only when he has something to say -- and at 33, he has been more vocal than ever. He was desperate to be heard. Those in charge at Barcelona didn't listen.

This is the story -- told with the help of numerous first-hand accounts from sources close to both player and club -- of how Messi's nagging doubts about Barcelona eventually became impossible to ignore, and what happened next.

Editors' note: This story contains reporting from Moises Llorens, Sam Marsden, Rodrigo Faez, Eduardo Fernandez-Abascal and Alex Kirkland.

ABOVE ALL OTHER CONSIDERATIONS both personal and professional, Messi's discontent stems from his desire to win. And for Messi, winning means the Champions League. Barcelona haven't done that since 2015. They haven't even come close. Embarrassed by Liverpool and Roma in recent years, the 8-2 humiliation at the hands of Bayern Munich at the quarterfinal stage of the competition last season, in August, was the tipping point. Messi is intensely aware of the impact Barca's European failings will have on his legacy. Four Champions League titles are more than enough for mortals. But not for Messi.

Several sources pinpoint one moment that best reveals Messi's disenchantment. It came at Camp Nou in May 2019. Barca were 3-0 up in the first leg of their semifinal against Liverpool. In the 96th minute, Messi -- who had scored twice -- drew three defenders before squaring the ball for an unmarked Ousmane Dembele. Dembele miskicked, Alisson made the easy save and Messi fell theatrically to the floor, face down in the turf.

He knew that Barcelona needed another goal -- the season before, Roma erased a first-leg, 4-1 deficit to advance on away goals to the semifinals -- because his teammates couldn't be trusted to defend a 3-0 lead away from home. Six days later, he was proved right.

"The last chance for Dembele was clear-cut," Messi told reporters after the first leg. "Four goals would have been better than three."

How do you prevent those mistakes from happening again and again? One approach might involve a clear-eyed vision of the kind of team you want to construct. But Barcelona's planning has been incoherent at best. Losing Neymar, with whom Messi loved to play, to Paris Saint-Germain was perhaps forgivable. Wasting almost €300 million on Dembele and Philippe Coutinho -- both yet to come good, three years on -- less so. The club failed to bring Neymar back last summer, signing Antoine Griezmann instead for a similar sum. Griezmann is a player who has failed to adapt for various reasons, including the fact his preferred position is taken by Messi.

A series of sporting directors -- Andoni Zubizarreta, Robert Fernandez, Pep Segura, Eric Abidal and Ramon Planes -- have come and gone over the past five years, all of them unable to implement an effective long-term strategy because they were never afforded the time to do so. They have all been made scapegoats by Bartomeu, sacrificed as symbols of the club's shortcomings. Among them, they brought in a mishmash of players recruited with different ideas in mind. New signings arrived, flopped and left. Legendary midfielder Andres Iniesta departed. Gerard Pique and Sergio Busquets got older.

Messi waited, despairingly, for things to get better.

EVEN AS BARCELONA FAILED IN EUROPE, they at least continued to win La Liga.

Manager Ernesto Valverde, despite his unpopularity among some Barca fans, won the league ahead of Real Madrid in 2018 and 2019. Messi liked Valverde. Sources told ESPN that the easygoing, diplomatic Valverde maintained relative harmony in a dressing room divided between two cliques: one, led by Messi, Luis Suarez and Arturo Vidal, who were essentially happy under the coach's laid-back regime; and another, including Marc-Andre ter Stegen and Frenkie de Jong, who would have preferred a more disciplined approach.

That balance endured until January this year when Valverde was sacked -- with Barca top of the league -- after defeat to Atletico Madrid in the Spanish Supercopa in Saudi Arabia. He was replaced by Quique Setien, a man with no experience managing a group of players at this level.

The fallout from Valverde's firing was damaging, too. Sporting director Abidal said in an interview with Sport in February that "a lot of players weren't happy [with Valverde] and weren't working a lot."

Messi, in a rare moment of rage, snapped. "I honestly don't like to do these things, but I think everyone should take responsibility for their decisions," he wrote on Instagram. "The sporting department should take responsibility. When you talk about players, you should give names. If not, you're tarnishing all of us and feeding things which people say and aren't true."

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Abidal touched a nerve. Messi is incredibly sensitive to the idea that he runs things at Barcelona, responsible for hiring and firing coaches and identifying transfer targets. It's understandable, even if it's hard to dispute the grain of truth at its heart: that Barca should do everything possible to keep their best-ever player happy.

Barca had been failing to do that on the pitch; they were failing off it, too. In February, it was alleged that a company the club had hired to protect its image was behind social media accounts posting disparaging comments about current and former players. Messi and his family were mentioned. It was another blow to his already fragile relationship with Bartomeu, even if Barca continue to deny any wrongdoing in the scandal that's come to be known as "Barcagate."

SETIEN HAD A BRIEF AND TROUBLED SPELL IN CHARGE. From the beginning, Messi was not impressed with him despite hyped-up claims of a return to the more attacking, possession-based style of play made famous at the club by Johan Cruyff and, later, Pep Guardiola.

An uneasy, six-month truce lasted until June, when La Liga returned after its pandemic-enforced break. When Barca dropped their first points in a frustrating goalless draw with Sevilla, sources told ESPN that there was a tense dressing room showdown between captain and coach as stunned teammates looked on.

The top-of-the-table lead that Setien had inherited from Valverde quickly disappeared. Real Madrid won 10 games in a row, while Barca dropped points in four of theirs. Their title challenge ended with a 2-1 home defeat to Osasuna on July 16. Speaking immediately afterward, Messi didn't hold back.

Things had "all gone wrong" since January, he said, in a blatant criticism of his new coach. "We've been a very erratic, weak, low-intensity team. Today's game is a summary of the season. We have to be self-critical, starting with the players but across the whole club."

BARCELONA HAD WON NOTHING IN 2019-20, their first trophyless campaign in 12 years. Setien was dismissed. His replacement was club legend Ronald Koeman, but it was too late. Messi's mind was made up. A first meeting between Messi and Koeman -- one that saw Messi interrupt his holiday with Suarez and Jordi Alba in the Pyrenees to return to Barcelona on Aug. 20 -- did not go well. Messi expressed his doubts and remained determined to leave the club.

Around the same time, he called Guardiola.

"Messi and Pep spoke for hours," a source told ESPN. The pair are close and have much in common. Messi, Guardiola and Manchester City all share an obsession with the Champions League. City have never won it; Guardiola and Messi are thought not to have won it often enough.

Messi knew that his options for leaving Barcelona were limited. Unlike Barca, he viewed City as having a clear strategy and an upward trajectory. The player told his former coach that he wanted to move. Guardiola said he would talk to decision-makers at City. It wouldn't be straightforward, he warned.

Messi's flirtation with City was nothing new. In fact, City's rebuild under their new owners over the past decade has been carried out with the aim of attracting first Guardiola and, later, Messi. There were discussions in 2014, and again in 2016. Yet City's hopes of signing Messi this summer were dependent on them playing in the Champions League. Once their two-year ban from European competitions was lifted on July 13, they knew they would be the front-runners to sign him if he left Barca.

There was never any direct contact between the clubs, nor did Messi's camp transmit directly to Barca a desire to move to City, but sources at the Catalan club say were informed of City's interest in signing Messi by a third party. It gave City a lot to think about. Could they afford Messi's salary? How much would they have to pay Barca? What about financial fair play? His €700m buyout clause was impossible, even for City. There was a more tantalising prospect, though: Messi might be available for nothing.

The mechanism by which they thought they could pull off a deal had existed for years. Messi's long-term doubts led his advisers to insert a release clause in his Barca contract when it was renewed in 2017. At the end of the 2019-20 season, within a defined period, he could unilaterally rescind his contract and walk away.

And so, Barcelona's board nervously waited. In the end, the date -- initially widely reported as May 31, later corrected to June 10 -- fell when La Liga was about to resume. Nonetheless, when it had passed, the club were quick to brief the media. As far as they were concerned, Messi would be staying until 2021. Messi has since said he didn't inform the club before then because they were still involved in La Liga and the Champions League; one source, though, says the fact City were banned from European football before winning an appeal also complicated his route out of Camp Nou.

The original date in Messi's contract had been drawn up to coincide with the end of the season. But with the campaign extended because of the coronavirus pandemic, Messi's camp felt they had some wiggle room when it came to the interpretation of the clause.

Sources told ESPN that the feedback Messi received from legal experts was mixed. Only one law firm out of at least four consulted, Cuatrecasas, believed the argument had a realistic chance of success. That was enough and Messi decided to go ahead. If he stood his ground, perhaps Barca would blink first.

AUG. 24 BEGAN WITH A PHONE CALL from Koeman to Suarez. In a conversation that lasted around a minute, the coach told Messi's best friend in the squad that he was not in Barca's plans and should look for a new club. Vidal received similar treatment. Messi's allies were being pushed out and, in his view, disrespected.

Later that day, Messi took action. On advice from Cuatrecasas, the player opted to use a burofax -- a registered letter, used when legal proof of receipt is required -- to inform Barcelona that he wished to leave for free, exercising his release clause. Signed by Messi, it was sent just after 7 p.m. By mid-morning on Aug. 25, the letter had arrived at Camp Nou.

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The first to read it, aghast, were Bartomeu and the head of Barca's legal department, Roma Gomez Ponti. "They could not believe their eyes," a source told ESPN. For them, there was no debate: The clause had already expired. "Put aside everything else you've been working on and focus on this," Bartomeu told the club's lawyers. Barcelona contacted two firms specialising in sports law -- Costa Torrecillas & Associates and Bufete Antras -- for advice. (The former had won the club a favourable judgment months earlier in their dispute with Neymar over a renewal bonus.) Both firms agreed Barca were in the right and should not give in to Messi's demands.

Despite that, sources told ESPN at the time there were board members who supported letting Messi go. Not for free, mind you, but if it meant bringing in a large fee and removing his €90m salary from the wage bill, the club might be able to dig itself out of a €300m financial hole during the COVID-19 crisis.

"Messi has so much power at the club, both on a financial and sporting level," one source said. Another, close to the dressing room, went further. "It's the moment to sell him, it's a historic opportunity to be able to change things. There are players who will perform a lot better without him in the team."

Those voices believed a managed departure could be beneficial, but the president would not entertain the prospect. It was €700m from a buying club, or he stays. "Bartomeu doesn't want to be the president who agrees to the sale of Messi," a source told ESPN, even as another source said, "it's the best thing he could have done."

Bartomeu might have ruined his relationship with Messi -- the player called him a liar, claiming Bartomeu had assured him he would let him go -- but he got his wish. In the end, he won't be the president who oversees Messi's departure; after all, the club's presidential elections will happen on March 20 or 21 next year, before Messi's contract expires.

AT MANCHESTER CITY, there had been a growing acceptance that signing Messi for free was impossible, so they turned their attention to a negotiated settlement. After several days of crunching numbers, a source told ESPN that "if Barcelona let him leave for €100 or 150m, Messi will be a City player." City were also willing to include players of interest to Barca, such as young defender and La Masia product Eric Garcia, in a deal, although ESPN was told that others, including Gabriel Jesus, Bernardo Silva and Riyad Mahrez, would not be included.

All of that depended on Barca being willing to budge. Messi waited and maintained his silence, even skipping coronavirus testing ahead of a return for preseason training with new coach Koeman. Board members who'd been critical of Messi felt he should be fined for that; Bartomeu believed doing so would escalate the crisis. As Barca drafted burofaxes of their own to correspond with their absent captain, sources told ESPN that some versions specified that there would be no punishment, while others left the option open.

On the morning of Sept. 2, Messi's father and agent, Jorge, flew from Rosario, Argentina, to Barcelona for a meeting with Bartomeu that evening, but no progress was made. Bartomeu had one important thing as leverage: Messi could not stomach a legal battle. He was determined to leave, but not if the process descended into lengthy litigation. City were reluctant to take that road, too.

Everything changed on Sept. 4. In an interview with Goal's Ruben Uria, Messi announced his decision to stay. "The president told me the only way to leave was to pay the €700m clause, which is impossible, and that the alternative was going to court," Messi said. "I would never take Barca to court because it's the club I love."

It could have ended differently. Some at Barcelona feel that Messi's approach -- both in law and in public relations -- was flawed from the start. "He didn't choose the best communications strategy," one source told ESPN. "If he had timed it better, he could have finished off Bartomeu and he'd be at Manchester City by now." In this reading, Messi's fundamental mistake was a failure to articulate his decision to leave sooner, and to speak directly to the fans -- perhaps, as many other players might have done, on their social media accounts -- before the burofax was sent.

Others question whether the prospect of another year of an unhappy Messi is best for Barca. The No. 10 has channelled his anger on the pitch before with positive results for the team; he might do so again. But ESPN has been told that some players thought a fresh start, with a new coach and without Messi, might have been the best for everyone.