Wolves lost the game 3-0 at Old Trafford as McCarthy stunned fans by making 10 changes in his starting line-up to the team that managed to beat Tottenham at White Hart Lane on Saturday.
“We had a great result on Saturday and in terms of exertion and how hard it was, they rate it every time and it was between nine and 10 on all the marks,” the Wolves boss told Sky Sports.
“That’s how much it took out of them (and) if they have another game of that magnitude – I don’t think we can cope with it.
“I’ve got 21 fit players, I’ve got three players just having operations – I need to protect them – we’ve got a lot of games coming up.”
McCarthy added on the game: “Some of it was good, some of it alright – I made changes (because) I don’t think we can do two nine-out-of-ten performances back-to-back then back-to-back again.
“I thought (Michael) Mancienne and (Andrew) Surman were outstanding and Kev Foley but at the end of it we’ve been beaten 3-0. But there is some pluses certainly.”