The Molineux boss believes that because his side played with just 10 men for much of the second half on Boxing Day when they lost 2-0 at Liverpool, they will find it tough against Roberto Mancini's outfit.
McCarthy said: "We played well at Anfield, I am proud of them. Liverpool did not make many chances but with 10 men the game is finished.
"Matt Jarvis was running on empty and Kevin Foley was too, they all put more than a shift in.
"I will have to look at them all to see who can play against City. But I wonder whether we can produce that level of performance again so soon after the Liverpool game.
"To recover from that, playing with 10 men, is very difficult. We just have to try to do our best now.
"Manchester City played on Saturday, they will be tired too. But they have a slightly bigger squad than I have. I will assess them all before making any decisions."