Celtic manager Gordon Strachan says he knows what went wrong after watching his side lose 3-1 to FC Copenhagen.
"Rest assured I know the problems and I will sort them out - don't worry about that," he said.
"The intensity of their play was excellent. Physically in the first half they won everything.
"We should've been celebrating with the fans here, but the defeat just wipes it away. I know how to make them better and I will do it."
Strachan said the players were subdued after the defeat - despite already having secured qualification for the knockout stages of the Champions League for the first time.
"Nothing can give us a lift at the moment and the disappointment overwhelms me," he said.
"We are down. You might point out that we are 16 points ahead in the title race but that doesn't affect us at the moment because we are overwhelmed with disappointment."
The Celtic boss was left to rue defensive errors in the first half as FC Copenhagen established a two-goal lead by the 27th minute.
"We were poor at set-pieces and we needed to deal with that. They scored from a throw-in, a free-kick and a corner," he said.
"I have no regrets. There were players like Thomas Gravesen, Jiri and Maciej Zurawski that needed games.
"But we struggled for shape in the first half and that improved when Shunsuke Nakamura came on."