The pair clashed on the training pitch this week.
And Mancini said: "The problem could be himself. (If) he doesn't change, for him it will be very difficult in the future - for him, not me.
"Mario could stay with me one day, one month, five years. He is 22 years old. He needs to change. His problem is for himself.
"It is not easy to manage him and we can talk about him, but my thoughts about him don't change.
"What he did yesterday he can do also during the game - this is the problem, but I have faith, yes."