A bid either now or at the end of the season would give the City board a dilemma but Mancini says he will fight to keep Mario for now.
He said: "No, we can't sell any players. My thoughts on this don't change.
"The owners always support me and, like me, they hope every day that Mario can change - to think only about his job and playing.
"He should understand that the career of a player is short.
"He is 22 but three, four and five years can pass in a second and I hope the day arrives when he understands his quality."