Mancini's side are currently three points behind rivals United, who they face next Monday at the Etihad Stadium.
Despite having the title race in their hands, Mancini believes that City are unlikely to overhaul United.
"They have three more points and they have a games not as difficult as us," Mancini told BBC Sport.
"I think that United is in the top, they have three more points and after the derby they have two easy games."
After the derby City face Newcastle United and Queens Park Rangers, while United face Swansea City and Sunderland.