Sinisa Mihajlovic believes teenage goalkeeper Gianluigi Donnarumma should stay and grow at AC Milan.
Donnarumma, 18, angered Milan fans after it was revealed he would not renew his contract beyond its expiry in 2018.
"Gigio is very strong, but he's still a boy," he told Sky Italia.
"To become a champion, he has to grow in an environment that loves him and can help him.
"There's no need to rush, although I understand [agent Mino] Raiola doing it for his clients.
"I would stay some more in gratitude to Milan, to grow and I think because they offered him a big contract.
"He now has half of Italy against him and that can be tough. The situation could have been handled better by both sides."
Donnarumma has already made four senior appearances for the national team, and played almost 70 times for Milan in the league.