AC Milan wonderkid Gianluigi Donnarumma ha rejected AC Milan's new contract as Real Madrid are believed to be preparing a bid for the goalkeeper.Donnarumma, tipped as the heir to Gianluigi Buffon and potentially the best goalkeeper in the world, has told AC Milan he will not renew his contract with the club and is expected to be sold this summer, according to the Independent.The 18-year-old keeper made his Milan debut at just 16, in a pre-season game against Real Madrid. And it is the Spanish giants who are most keen to take him away from San Siro with Florentino Perez dropping his interest in David De Gea last month.Donnarumma's agent, the controversial Mino Raiola, was locked in talks with Milan on Thursday afternoon but when Marco Fassone, Milan's chief executive, emerged, he had a bombshell for the club's supporters. “Raiola informed us that Donnarumma has made a definitive decision not to renew the contract with Milan. It is a definitive decision, made by the player. I want to remind you all that 10 days ago (director Massimiliano) Mirabelli made a significant contract proposal to the player, one even bigger than the reports that appeared in the various papers.“The player evaluated it and made some judgements that were not just economic, but also technical and professional, and he told us that he does not wish to renew the contract, so his time with Milan will therefore conclude by June 30, 2018.“We were taken by surprise, as we had confidently hoped Donnarumma would be the goalkeeper taking Milan into the future that we could build the team around. “We trust that we can do our best. Naturally, the decision leaves a bitter taste in the mouth, but now we have to go forward and Milan go forward.” said Fassone on The IndependentIt is a hammer blow for Milan, who had begun the summer's transfer window better than any club on the planet. In securing four high-profile signings of players who will grow at the club and help restore them to the upper echelons of Serie A, it was hoped that Milan had demonstrated to the teenaged Donnarumma that they were ready to compete again and return to greatness.Instead, the young keeper is mulling over an offer of £5m per year from Madrid as they work out how to strike a deal with the Rossoneri to add their latest galactico into the mix.