I don't think he will play a weak team in either game.
Both games are vital.
I don't think both are vital. Having got 3 points away at Chelsea, I'd say the cup game is of greater importance now.
Lose the cup game and we're out of it, with only one more realistic chance of a trophy.
Lose against city and it's disappointing but no big deal. We might be expected to lose against them anyway. If we lose and miss out on 4th place by 3 points, it won't be because we lost to city - it'll be because of the draws against Norwich and Swansea.
Hence I would suggest that we need to decide who we want to play against Chelsea in the cup, and then decide which of those players can also play in the City game 2 days before.