Gianluigi Donnarumma must publically explain why he will not be signing a new contract with AC Milan, says two-time European Cup winning goalkeeper Giovanni Galli.

The Serie A club announced on Thursday that Donnarumma's agent Mino Raiola had told them the highly sought-after 18-year-old will not be signing a new contract at San Siro.

With his current contract at San Siro due to expire after the 2017-18 season that leaves Milan in the tough position of either losing their prize asset for nothing or selling him during the transfer window.

Donnarumma has been linked with the likes of Real Madrid, Juventus and Manchester United and his departure now appears inevitable.

Galli – who won two European Cups with Milan and the Serie A title in 1988 – was shocked by the decision and demanded explanations from the Rossoneri's young shot-stopper.

"I want people to realise, and all agents to realise, that we are talking about Milan here and not any old club," he told Mediaset Premium.

"This club has won seven European Cups and represents Italian football. There must be respect for a club that has given a teenager this incredible opportunity to play regularly in Serie A.

"If he wants to earn more, that's one thing, but saying he won't sign a renewal regardless of the terms is not fair. At this point, I want to know the real reasons he is not signing a renewal.

"Donnarumma is 18 now, he's an adult, so he has the right and above all the duty to explain his decision."