Balotelli has had a false start to his City career due to a knee injury.
But Mancini told the Daily Mail: "Balotelli I have known since I gave him his debut at 17. He may have changed as a person in the last three years but he is a fantastic player and he works 100 per cent.
"Outside the pitch, he does things and it might be better he did not — but he is 20. I do not know too many perfect 20-year-olds. I was never perfect when I played, either. Good players are not perfect."