Manchester United manager David Moyes says he is to blame for his side's 2-0 loss to Champions League opponents Olympiakos on Tuesday.
United were favourites to beat the Greek side over two legs but they now face the prospect of missing out on the quarter-finals.
"I take responsibility," said Moyes. "It's my team and I always front up."
The Scot added: "It was a really poor performance. We never really got going and we didn't deserve anything."
United registered their first and only shot on target of the match in the 89th minute as they slumped to a surprise defeat.
Moyes, who left teenager Adnan Januzaj out of the squad, admitted they had not done enough to secure a potentially valuable away goal.
"I am just surprised," he added. "I didn't see that level of performance coming, I just didn't see it.
"It's the worst we've played in Europe. We didn't offer enough on the night to create a goal.
"There is undoubtedly talent at Manchester United but we didn't show it."
Striker Robin van Persie, who failed to take United's best chance of the night, also spoke of his frustration.
He told Dutch broadcaster NOS he found it difficult to receive the ball: "Our fellow players are sometimes occupying the spaces I want to play in. When I see that it makes it difficult for me to come to those spaces as well.
"That forces me to adjust my runs, based on the position of my fellow players. And unfortunately, they're often playing in my zones. I think that's a shame."
Asked about his manager being under pressure, Van Persie added: "We all have to work at it. In some games we do play well but in others we do not. We have not had luck at times. I am not going to point the finger at anybody.
"We need to try to turn it around and we need to take our chances. With all due respect to our opponents, we should be able to win by three goals."
The last time United overturned a two-goal aggregate deficit in Europe was 30 years ago, when captain Bryan Robson led them to a 3-0 win over Barcelona at Old Trafford in the last eight of the now-defunct Cup Winners' Cup.
The second leg is on Wednesday, 19 March.
"We are determined to put it right and we have the opportunity to do that," said Moyes.
"The players are hurt. Old Trafford has seen some great nights in the past and we hope to see another one."
Olympiakos manager Michel insists the tie is very much alive as his side chase their first appearance in the last eight since 1999.
"I'm obviously very happy with this match, but most of all I'm proud of my players," he said.
"But if somebody says that 2-0 is enough to qualify, he's probably wrong. We have a 2-0 lead against Manchester United, which means nothing."