MANCHESTER, England -- It could have been a week that proved Manchester United are on the right track under Ole Gunnar Solskjaer, but instead their season is in danger of derailing.

A 3-2 defeat to RB Leipzig on Tuesday was enough to cut short United's return to the Champions League, and they will be back in the Europa League in the new year. On Monday, Paul Pogba's agent Mino Raiola dropped the bombshell that the France midfielder will not sign a new contract and wants to leave the club at the earliest opportunity. Manchester City, visitors to Old Trafford on Saturday, are waiting in the wings to make it a hat trick of crises.

Pogba was left on the bench for the make-or-break clash against Leipzig -- Solskjaer insisted before kickoff the decision had nothing to do with Raiola's explosive interview with Tuttosport, which was published just as the players landed in Germany on Monday evening -- but by the time he was introduced after an hour, United were already 2-0 down and well on their way to an early exit.

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"We didn't perform as a team well enough and that's always the manager's responsibility, to get everyone ready," said Solskjaer afterwards. "We knew they were going to come at us, we knew they were going to put crosses in the box and unfortunately we conceded two goals and never got going."

United remain steadfast in their belief that Solskjaer is the right man for the job, but there will be questions asked about how his team have managed to be eliminated after starting the campaign with victory at Paris Saint-Germain and a 5-0 demolition of Leipzig. Ultimately, they have paid a high price for the 2-1 defeat to Istanbul Basaksehir that looks even more ridiculous now than it did on the night. Paul Scholes branded the result in Turkey "a disaster."

Solskjaer is the first manager to lose six of his first 10 Champions League games in charge of an English club, but he is not in any immediate danger having built up enough goodwill with executive vice-chairman Ed Woodward and owners the Glazers. However, he will know enough about the club's recent history to be aware that when Louis van Gaal's United were knocked out of the Champions League with a 3-2 defeat to Wolfsburg in 2015, it was the beginning of the end for the Dutchman. Six months later he was replaced with Jose Mourinho.

Mauricio Pochettino would have been forgiven for allowing himself a small smile as he continues the search for his next job. Leipzig coach Julian Nagelsmann and PSG boss Thomas Tuchel, the two managers who will progress from Group H at Solskjaer's expense, would also be in the frame, but United are not at that point yet.

Solskjaer, though, should be worried that he asked his key players to step up ahead of a crucial game and they did not. Even more concerning was captain Harry Maguire admitting they "weren't it at" from the start of the biggest game of the season.

Needing only a point to qualify, Solskjaer picked a back five that included Luke Shaw, handed his first start for more than a month after recovering from a hamstring injury. But for 30 minutes it was hard to tell if United were playing five defenders or none at all.

Former Manchester City full-back Angelino took advantage of Aaron Wan-Bissaka's complete lack awareness at the back post to make it 1-0 after two minutes. After 12 minutes, it was 2-0 when Shaw went AWOL and Amadou Haidara was left with a simple volley past David De Gea. Emil Forsberg should have made it three shortly afterwards when United's back five decided the Sweden forward wasn't worth marking at all before VAR came to their rescue when Willi Orban's tap-in was ruled out for offside.

The only positive from a disastrous first half was that it wasn't quite as disastrous as it should have been.

Maguire and De Gea added their names to roll of dishonour by somehow combining to allow Justin Kluivert the simplest of finishes to make it 3-0 after 69 minutes, and although United rallied with goals from Bruno Fernandes and Pogba in the final 10 minutes, it proved one comeback too far.

Pep Guardiola is in for a treat when it comes time to analyse the defending ahead of this weekend's Manchester derby. United have conceded the first goal in eight of their 10 league games and three of their six Champions League games, and although it has allowed for some thrilling comebacks, it is not a sustainable strategy for success.

"In other games where we conceded the first goal we started pretty well but today we just didn't turn up until they scored the second goal, suddenly then we started playing again," said Solskjaer. "The second half was one-way traffic more or less and the one chance they had they managed to score. 3-0 down is difficult but they all gave everything, good character and effort. I can't fault anyone and we were close to getting the third and that would have been some achievement against a good team like Leipzig."

It leaves Solskjaer with the task of picking up his players ahead of the first derby of the season while again setting about rebuilding his reputation with supporters who are still doubtful he can return United to the top. It could have a been the week to prove he is capable of scaling those heights, but after a chastening Champions League exit, the Norwegian has got a mountain to climb.