Pep Guardiola believes physical tiredness had nothing to do with Manchester City's 2-1 Champions League defeat at home to Lyon on Wednesday.
"I don't believe in the physical condition [as an excuse] in my point of view," he said ahead of Saturday's trip to Cardiff back in the Premier League.
"I believe the mental condition controls everything you do on the pitch, what you do when you have the ball, what you do when you don't have the ball, how you defend set-pieces.
"They [the players] are young, they train every day and we take care of them.
"It is not like the Premier League, when you have another game, another game. Here, every game is like a final. There is a short group stage - one or two mistakes and you are out.
"But we still have five games [in the group stage] and we are going to prepare well when we go to Germany to make a good game."