Roberto Mancini expects a month to test his team to the full in the wake of a second stunning cup defeat in four days at Etihad Stadium.
City's Carling Cup ambitions are in peril after Steven Gerrard's penalty decided a semi-final first leg with the Blues badly missing Vincent Kompany, David Silva and Yaya Toure.
Mancini is hoping that Silva, who injured an ankle in the first half of Sunday's FA Cup derby defeat, will be fit to face Wigan in the Premier League match on Monday night.
But Kompany is banned for three more games and Toure will still be on international duty when title pursuers Tottenham turn up at the Etihad on 22 January.
Blues boss Mancini said: "Tonight we played without three or four important players for us and it was difficult. We will be like this for one month.
But I always believe we can win. They won here this evening, we can win there in 14 days
"Against United it was a strange game. Tonight we were poor in the first half, but we played very well in the second. We had the chance to score but we didn't."
Gerrard's 12th-minute spot kick, awarded for a foul by Stefan Savic on Daniel Agger, turned out to be the difference. Mancini said: "It was probably a penalty, yes. I agree with it."
Just to add to Mancini's problems, Mario Balotelli limped off in the first half, the manager revealing he has had an ankle problem for the past ten days.
As for the badly-missed Silva, he added: "Tomorrow we will see if he can play against Wigan. I don't know how he will be."