The Frenchman has endured a largely bit-part role with the Premier League champions this season and has been omitted from the last two starting lineups.
However, Mancini is backing the former Arsenal man to turn his fortunes around.
"I think that he can do better because he has quality, technique and he's strong," Mancini told ESPN.
"For me, Samir is a top player and a top player should play well in every game.
"Samir is one of the best players in England. He showed this with Arsenal, he showed this with us last year and also this year sometimes."
City travel to Villa Park to face Aston Villa on Monday night.