It's been a long time since we've seen so many high-profile moves in one month, but the 2021 summer transfer window saw the game's two best players of the modern era, Cristiano Ronaldo and Lionel Messi, join new clubs. Ronaldo made a sensational return to his former club, Manchester United, after three seasons at Juventus, while Messi left Barcelona as a free agent once talks broke down over a new contract, signing with Paris Saint-Germain less than a week later.

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Yet both stars have found that so far, the grass isn't always greener when it comes to major changes. Ronaldo has been superb as a player for United (nine goals in 12 appearances), but the club has been stuck in a spiral of poor form, with just one win in the Premier League since mid-September. Meanwhile Messi and PSG are already 10 points clear in Ligue 1 and are cruising towards the Champions League last-16 (with Messi scoring three times), but the Argentine star has yet to score in the league (five appearances) and has suffered several frustrating minor injuries along the way.

With over a third of the European club season already in the books, ESPN's Mark Ogden (Ronaldo) and Julien Laurens (Messi) look at the situation for both superstars at their new clubs.

Jump to: Season so far | What's working/not working | Right move?

The season so far

Ronaldo: Two goals on his debut in a 4-1 win against Newcastle gave Ronaldo a dream start to his second spell at United. While the team's results have been inconsistent since Ronaldo returned -- 5 wins, 6 defeats and 2 draws -- his individual contribution has been little short of remarkable, with 9 goals already and some of those proving to be crucial late winners or point-savers.

Ole Gunnar Solskjaer substituted Ronaldo while drawing 1-1 against Young Boys, and the switch was followed by the Swiss team scoring a late winner, while the manager also dropped him to the bench for the home draw against Everton.

But in terms of highs and lows, Ronaldo has delivered time and time again for his team. The only lows have been the team's poor results, which have left Solskjaer fighting for his job. Without Ronaldo's contribution, Solskjaer may not have survived so long.

Messi: So far, Messi in Paris is the story of a glass half-full or half-empty. If you look at it from a Ligue 1 perspective, it's the latter: 5 games, 349 minutes, 0 goals, 0 assists, 15 shots (4 on target), 1.47 expected goals, 1 big chance created, hit the woodwork 3 times, 1.6 successful dribbles per game. There's a sense that he's still adapting to his own team and to the French league as well, which is much more physical than LaLiga.

If you consider his arrival in the context of the Champions League, it's half-full: 3 games, 289 minutes, 3 goals (a wonderful counter attacking one against Manchester City (2-0) and the winning one against RB Leipzig (3-2) with a delightful Panenka), expected goals 2.40, 9 shots (5 on target), 3.7 successful dribbles per game. Messi knows the Champions League, and that could be enough to explain his domestic struggles, where teams who face PSG are very often a compact low block.

What's working, or what's going wrong?

Ronaldo: There are two contrasting views on Ronaldo at United. The first is that his incredible goal record makes it worth the tactical problems that his presence in the team can cause, such as his limited defensive contribution and an earned sense of selfishness once he has a sight of goal. Ronaldo usually always delivers, so you take the rough with the smooth.

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The alternative outlook is that Ronaldo upsets the balance of the team and without him, United would arguably be a stronger unit and the goals would be spread more evenly throughout the side. It's also a reality that Solskjaer has struggled to devise a formula to make his team robust enough defensively when Ronaldo, Bruno Fernandes and Paul Pogba have played together.

By trying to accommodate all three players, Solskjaer has left his defense exposed too often. Also, Pogba's bright start to the season halted once Ronaldo arrived and Fernandes, as has happened with Portugal, is not as influential as he was prior to Ronaldo's return to United.

ESPN reported earlier in October that Ronaldo has urged Solskjaer to find a way to get the ball to him quicker in attacking areas, and sources have also said that the lack of understanding between Ronaldo and Mason Greenwood is causing concern, although the youngster created the 36-year-old's crucial late equaliser against Atalanta in midweek.

In truth, Ronaldo has been a positive and negative for United so far, but the positives heavily outweigh the negatives. Yes, there are tactical issues to address, but that is the job of Solskjaer -- not his most famous player. Ronaldo has simply done what he was signed to do, scoring goals and making decisive contributions in big games. Sources have said that his sheer professionalism and desire to continually improve has started to drip-feed into the squad, and that he remains a humble character around the training ground despite his star status.

Messi: As amazing as the Argentine is, it was always going to take time for him to adapt to the biggest change in his life since he was 13. Back then, he went from Rosario to Barcelona. This time, it was a much shorter journey from Catalunya to the French capital, but it's still a very different life. Even the traffic in Paris is much heavier than in Barcelona, to the point that it surprised the Messi family!

On the pitch, this is a new team with a new manager (Mauricio Pochettino) who is himself still searching for the right tactics and the right way to bring all PSG's star power together. It took Ronaldo four league games and more than 20 shots before finally finding the back of the net for Juventus after his big move from Real Madrid in 2018.

For Messi, it is taking time as well. He has been at his best when playing more centrally behind Kylian Mbappe, instead of being stuck on the right wing alongside the touchline, where he no longer has the energy or pace to impact the game further from goal. Messi needs to be involved and for that, playing centrally is much better for him. He has been more dangerous, even in Ligue 1, when he played more through the middle.

It also helps the team massively when it comes to beating the opposition's press. Obviously, his lack of defensive work has been noticed, too, and the team still has to find the right balance in defensive transitions.

Messi has also been hampered by lingering minor injuries that have hindered his adaptation. He's already missed half of PSG's league games this season and was not been involved at all against RB Leipzig or Bordeaux in the Champions League and Ligue 1 respectively.

Was it the right move?

Ronaldo: Would the Portuguese superstar have been a bigger hit at Manchester City? He certainly would have scored plenty of goals and been more likely to win a major trophy this season, but United is in his DNA and it would have been an awkward fit had he pulled on a blue shirt rather than red.

The fact is, United are not at City's level yet and they need a talisman in a way that Pep Guardiola's team don't, which is why United is the perfect fit for him. Ronaldo wants to be the centre of attention and the player who makes it all happen. He also wants to be the hero and he has already filled that role on several occasions for United.

He would have enjoyed more success as a City player, but there is a sense that his second spell at United will prove more rewarding on a personal level than whatever he could have achieved at the Etihad. It just depends on whether Ronaldo ultimately wants to be judged on trophies or something more difficult to quantify.

Messi: Simply put, it was Messi's only option. From the moment Barcelona informed him they could not keep him, PSG was the only new viable destination. However, it did fit perfectly with what the six-time Ballon d'Or winner wanted: a club capable of paying his huge wages, a very strong team where he could win another Champions League after lifting it in 2006, 2009, 2011 and 2015 with Barca, a place where he could play with friends and former teammates (Leandro Paredes, Neymar, Angel Di Maria) and where the manager would understand him (Pochettino), a city where his family would be happy and a club where the Messi brand could keep growing.

Paris and Messi are a great match on paper. After a rocky start, the onus is on both sides to make it work and optimise this incredible opportunity.