The Barclays Premier League champions were well below par and required a brilliant late Carlos Tevez goal to snatch a 1-0 victory against a superior Wigan side at the Etihad Stadium on Wednesday night.
Platt felt the team's exertions of the past week had affected performance, the game coming after a demanding derby win at Manchester United and an energy-sapping FA Cup semi-final success over Chelsea at Wembley.
He believes the toll on the players was as much mental as physical and he knows they must recover for a game important in the fight for second place at White Hart Lane on Sunday.
Platt, the first-team coach at Eastlands, said: "I think we are probably feeling the effects of the two big games we have had, mentally more than anything, what it takes out of you.
"We saw on the pitch we couldn't get anything going. There was a lack of energy about us. Maybe we were mentally tired.
"We played against a team that keep the ball and made it difficult for us.
"We didn't look as though we were going to create anything and I think it needed a flash of brilliance to unblock the game, but that is what we know we have got in the team.
"The physical side is one thing but we can recuperate by fuelling the boys right, getting the right food into them, giving them the right rest and the right cures.
"It is not the physical side that is the problem, but the mental side. That game will have brought us back to earth. We will recuperate and go to White Hart Lane."