"That is the only reason why Shay has not played so often because he is a fantastic goalkeeper."
Veteran midfielder Patrick Vieira is in a similar situation having started just two Premier League games this term, although he has made eight appearances in cup competitions.
The Frenchman, also 34, is one of a several fringe players that could come in at Eastlands as City look to secure a fourth-round trip to Notts County.
"Patrick Vieira is an important member of our squad," said Mancini. "He is a good player, who has lots of experience.
"He will probably play, along with Jerome Boateng, James Milner, David Silva, Jo and Joleon Lescott. We have other players that we can win this game.
"I don't like this replay because we have a lot of matches to play until the end of the season already," he added.
"But we want to win because we want to get to Wembley. For me, that is very important."
City are firmly in the Premier League title race and have reached the Europa League knock-out stage and although they made a tame exit from the Carling Cup, this year's FA Cup represents a great opportunity for the Blues to win their first major trophy since 1976.
