But this season, they are once again in the Europa League. And after a 1-1 draw with FC Twente, the "Red Devils" showed all the qualities of a Europa League team.
Twente are currently fourth in the Eredivisie and are one of the lowest seeds in this season's Europa League. They will be delighted with the draw against Man United. Meanwhile, the 4,000 Twente fans at Old Trafford celebrated as if they had won.
This will be a timely warning for Erik ten Hag ahead of three important games against Tottenham, Porto and Aston Villa. If things don't go well, questions will arise over Ten Hag's position.
Ten Hag said he did not want to face his former club because "it's not good to hurt something you love". In the end, it was Twente who caused Ten Hag pain.
"We let them take control of the game when we were 1-0 up. The players did not score a second goal to end the match. And then we were punished by our own mistakes.
This is the fault of the whole group. Twente players could lead the ball through the pitch without being stopped. We were too complacent, the players lacked ambition in the second half and had to pay the price" - Ten Hag said after the match.
Playing in the Europa League for the third year at Old Trafford may not be in Ten Hag's plans. But whether he likes it or not, he needs competition at this level. Under pressure from last season's 8th place in the Premier League, Ten Hag is smart enough to understand that he is not in a position to give up any competition.
And while Ten Hag wants to give key players like Diogo Dalot and Bruno Fernandes a break, he cannot take any risks. In the second half, the Dutchman was forced to send Rasmus Hojlund and Mason Mount, both of whom had just returned from injury, onto the pitch to find a goal.
In the immediate future, Man United need to get through the first phase of the new format. Perhaps by the time the knockout round takes place in February next year, Ten Hag's side will be in such a good position in the Premier League that the Europa League will no longer be a priority.
However, there is no such luxury at the moment. They need results and performances in every tournament, especially the arena with a chance to return to the Champions League.
Returning to compete in the Champions League alongside teams like Real Madrid, Bayern Munich and Manchester City is certainly the minimum requirement in Ten Hag's first year under Sir Jim Ratcliffe.
To do that, the "Red Devils" need to score more goals. After failing to score in a draw with Crystal Palace, Man United had 19 shots against Twente but only Christian Eriksen scored in the first half. Their Premier League record is also just five goals in five games.
Man United are one of the brightest candidates for this year's Europa League championship. With no team relegated from the Champions League in the new format, their biggest challenges are Tottenham, AS Roma and Eintracht Frankfurt.
At the end of the season, Ten Hag hopes Man United can once again call themselves a Champions League team, no matter how they achieve it. But now, the Old Trafford team will have to accept the Europa League. And Twente have proven that, for now, Man United belong in this tournament.
