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The Italy international's future has long since been the subject of speculation as he nears the end of his contract.
Milan director Maldini on Thursday (AEST) revealed the 22-year-old is on his way out of the Serie A club.
He said in a live streaming event on the Rossoneri's Twitch channel: "I think we should thank all the players who contributed to this incredible season.
"Gigio was a leader and often the captain. People sometimes don't realise what it means to be a professional, it means you must be ready to change club.
"It's difficult to accept, I realise, but it's also increasingly difficult to spend a career with one team. We must respect those who gave so much to Milan and remember Donnarumma did not disrespect us.
"It can happen that at times you have to take different paths. I can only wish him the best."
Donnarumma has been linked with the likes of Juventus, Barcelona and Manchester United.
Lille's Mike Maignan is reportedly set to replace Donnarumma at San Siro.