After falling 12 points behind leaders Manchester United in their bid to retain their Barclays Premier League crown, the knockout competition appears to represent City's most realistic hope of silverware.
Mancini may have rubbished suggestions he could face the sack if beaten by the Championship outfit in their fifth-round tie, but he remains aware of the game's importance.
After starting the season with such high hopes in the Premier League and Champions League, he is anxious to ensure the campaign does not disintegrate.
The Italian said: "We play with the best team. I will do some changes because I have two or three players injured but after that, I will play with the best team."
Although captain Vincent Kompany will not be risked as he continues his recovery from a calf strain, the only deviation in that policy will see back-up goalkeeper Costel Pantilimon given a chance.
Mancini said: "I will play Costel like always in the FA Cup. Costel is a good keeper, he deserves to play. He always does in the FA Cup and he did well against Stoke."
First-choice Joe Hart will therefore be rested but Mancini stressed that has nothing to do with the much-highlighted error the England goalkeeper made in last week's damaging loss at Southampton.
He said: "For a keeper it's normal sometimes to make a mistake. If the keeper makes a mistake you lose a game but if the striker doesn't score a goal, maybe you can draw 0-0.
"Their job is difficult because of this."