Thierry Henry believes that his Monaco side "stopped playing" after missing an early chance in a 4-0 defeat to Club Brugge that saw them crash out of the Champions League.
Sofiane Diop had a great opportunity to preserve Monaco's slim hopes of staying in the competition, but Brugge goalkeeper Ethan Horvath made a superb save.
That was the only chance Monaco – who sit second bottom in Ligue 1 and face runaway leaders Paris Saint-Germain next – manufactured, however, as the visitors cruised to a first Champions League victory in 12 attempts.
Goals from Hans Vanaken, Wesley and Ruud Vormer condemned Monaco to their heaviest home defeat in Europe's elite competition, with Atletico Madrid's win over Borussia Dortmund subsequently ending any chance of progression.
And Henry, whose side are now without a win in 15 games across all competitions, revealed his concern over Monaco's mentality.
"The score does not really reflect the face of the match but in the Champions League if you do not score you find yourself in this situation," he told a news conference.
"Despite our good start we failed to score. After we concede three goals in 12 minutes, it's a blow. As soon as we missed [the chance] we stopped playing.
"I am upset with the way we reacted to falling behind. We started well. But once we fell behind we stopped playing and that's a little bit worrying."
Monaco's misery was further compounded by Kamil Glik sustaining an injury, although Henry insists that his faith in the club's youngsters is not misplaced.
"We lost another player to injury in Glik. That's not going to help matters as we already had 10 or 11 injured players," Henry added.
"I have to be positive, otherwise what can you do? The performance of [Han-Noah] Massengo off the bench pleased me.
"Sofiane Diop was still good and Moussa Sylla. The young people are pulling us up."
Brugge boss Ivan Leko, meanwhile, emphasised the importance of a historic victory for the club, who remain in with a chance of progressing heading into the final two group fixtures.
"This is a big success. Not only because of the result – the quality of our football was very good too," Leko said.
"This is also important, not just the result. Now we are finally getting the rewards [for our good play]. This is historic."
