Celtic manager Gordon Strachan blamed himself after his side crashed 3-0 to Benfica in their Champions League match in Lisbon.
A nightmare first half for Celtic defender Gary Caldwell helped the Portuguese club to take a two-goal lead from which the Hoops never recovered.
The Scotland international scored an own goal after just 10 minutes and then his mis-placed header from a long kick by Benfica keeper Quim 12 minutes later allowed Nuno Gomes to grab a second.
A strike by substitute Andrei Karyaka in the 76th minute sealed the victory and brought Benfica to within two points of the second-placed Glasgow club with two matches remaining.
Copenhagen beat Manchester United 1-0 at home to join the Portuguese club on four points and Celtic, who have six points, play Sir Alex Ferguson's men at home on November 21.
However, Strachan pointed the finger of blame at the collapse in Lisbon not just on Caldwell or indeed his players, but everyone involved in a miserable night including himself.
Strachan said: 'I can't explain it. It was a poor performance as a group.
'When I say that I mean myself, the coaches and the players and we are not happy.
'We will analyse it but we will have to be honest about it. Tonight was a real test and we didn't come up to it.
'But we will bounce back, we have before.
'There are now three teams going for second place in the group but we are still second favourites to go through.'
Speaking about the luckless Caldwell, Strachan said: 'He's fine. All the players are a bit down.
'You can get individual mistakes but sometimes it's because players are put in that position.
'But we will share it as a group. We knew that they would come at us and that it was going to be high-tempo.
'But in the first half I didn't think they made too many chances. It was when we went with two men up that they started to make the bulk of their chances an maybe we didn't handle it as we should have.'
Benfica manager Fernando Santos, who was confident his side would win even after they lost 3-0 in Glasgow a fortnight ago, insists the section is now wide open.
He said: 'I wasn't surprised. Celtic are a great team but we were superior and it was a more just result than the first game (in Glasgow) - that wasn't fair.
'It was a different game, we were the home side but we still have respect for Celtic.
'Copenhagen are back in it and it is now a more open group. But we shall see what happens in the next two games.'