City are prioritising the Champions League, in which they play Dynamo Kiev on Wednesday, their manager Manuel Pellegrini said.
"We have just 13 players available to play and have to play the Champions League on Wednesday," he told a news conference.
"We’ll see the best team we can play on Sunday (at Chelsea).
"I always try to play with a strong team in every competition. They are all important but we must prioritise the Champions League.
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"For me always the priority is the next game but we must make an exception now because of so many injuries. After that, we have to play a really important 180 minutes (over two legs) against Kiev."
The Chilean added that it was difficult for a leading club to cope with a long run in the FA Cup as well as the Capital One (League) Cup -- in which City play Liverpool in the final on Feb. 28 -- because league matches had to be postponed.
He is also unhappy that the Chelsea game was moved from Saturday to Sunday for live television coverage, giving his team less time to prepare for the trip to Ukraine in the Champions League.
"Something is not correct with the Cup -- if you continue to the final, you have to postpone three Premier League games and then fit them in later," he said.
"And in every other league they try to help teams that are in the Champions League. Here you must do that also if you want to be successful in Europe."
Chelsea played their Champions League tie away to Paris St German on Tuesday.
Their interim manager Guus Hiddink, who won the FA Cup during his previous spell in charge in 2009, is adamant they will be going all out to lift the trophy for the fourth time in eight seasons. They also won it in 2010 and 2012.
"We have a serious approach to the FA Cup," the experienced Dutch coach told a news conference.
"It would be beautiful for everyone (to win it again). When springtime comes the big clubs must be there when the prizes are handed out."
Hiddink warned that any young players City pick "will be going 120 percent".
He added that injured captain John Terry will again be missing but should be fit next weekend.
(Reporting by Steve Tongue; editing by Toby Davis)
