Ole Gunnar Solskjaer admitted Manchester United were given a "reality check" as his unbeaten record as interim manager was ended by Paris St Germain.
The French heavyweights were shorn of Edinson Cavani and Neymar for the first leg of this Champions League last 16 tie but still proved too strong for United as Presnel Kimpembe and Kylian Mbappe secured a 2-0 win at Old Trafford.
Defeat for the Red Devils was compounded by the late dismissal of Paul Pogba, who will miss the second leg at the Parc des Princes, and Solskjaer was open that there was a gulf in class between the sides.
Nevertheless, Solskajer, who presided over 10 wins and a draw in his first 11 fixtures, insists United must learn from such setbacks if they are aspiring once again to be among the cream of the European elite.
He said: "We weren't at the level. This is a level up from what we have played against with the games we've had.
"We've had a great run, we came into this game in a great frame of mind, great form but of course it was a big step up, they have quality from the keeper to the striker.
Ole: "It's not going to be a season-defining one for us. It has to be one that we're going to learn from." #MUFC #UCL pic.twitter.com/bp6FZojKLA — Manchester United (@ManUtd) February 12, 2019
"There is a reason behind them being one of the favourites for the Champions League. That's the level we need to aim for at this club.
"Of course it's a reality check. The top four is one thing but we want to be at the top and Manchester United should be at the top.
"This is a top, top team that we played against. Our players are disappointed after the game, of course, but I also think they know that we need to step up our level to get to the level that we want to get to."
United held their own in the first half but were forced into a reshuffle because of injuries just before the interval to Jesse Lingard and Anthony Martial.
Alexis Sanchez was introduced at the beginning of the second half but was once again unable to impose himself as his struggles in a United shirt continued.
Solskjaer was in no mood to pull his punches with the Chilean, saying: "I can't do anything about Alexis Sanchez. When he plays he needs to find himself because we know there's a quality player there."
Solskjaer wants United to put the defeat behind them with fixtures against Chelsea and Liverpool in the FA Cup and Premier League respectively up next.
He added: "You can't feel sorry for yourself. Whoever feels sorry for themselves will not play probably against Chelsea."
United could face a UEFA probe after it emerged unpopular former winger Angel Di Maria was struck by a bottle thrown from the crowd. PSG could also be in trouble as an item landed at the feet of Luke Shaw in the first half.
Di Maria was the architect of PSG's victory, providing the corner that allowed Kimpembe to open the scoring in the 53rd minute before teeing up Mbappe on the hour.
PSG head coach Thomas Tuchel thought his Argentinian forward had been below par before the interval but was delighted he delivered a stunning riposte in the second half.
He said: "In the first half it was a bit hard for him playing right in front of me and losing many easy balls. He had a bit of a hard time because I was close to him.
"Maybe he was a bit nervous and a bit overused because he plays all the time for us.
"I'm happy he stayed confident, he's always super reliable, he always gives his best and for that it's easy to forgive him when he has not such a good first half.
"It's always dangerous for him from the corners and of course a superb assist, it was a perfect pass for Kylian. It was a nice comeback for him, I'm very happy for him and of course he helped us a lot."
