Gianluigi Donnarumma was at the centre of controversy during the summer, after it looked as if he was set to leave San Siro.
However, after long talks that eventually saw the 18-year-old put pen to paper on a new contract with the Rossoneri, super agent Mino Raiola has noq claimed that the club haven't kept a promise they made to his client.
Despite strong interest from Juventus and Real Madrid, Donnarumma signed a new deal with AC Milan that is littered with clauses that could still see the Italian international leave the club next summer.
"I've got nothing personal against [Marco] Fassone and [Massimo] Mirabelli, I just don't believe in their project," Raiola said, as reported by , according to La Gazzetta dello Sport.
"When all of Italy was panicking about the future of Donnarumma, they offered the captain's armband without us asking for it. All I can say is that there was a promise which has not been kept."
Donnarumma started for AC Milan in their humiliating defeat at the Stadio Olimpico on Sunday. Lazio's Ciro Immobile scored an impressive eight-minute hat-trick to guide the Biancocelesti to a 4-1 victory, with former Liverpool star Luis Alberto rounding off the scoring for the hosts before Riccardo Montolivo registered a consolation goal for Milan.
Speaking after the defeat, new captain Leonardo Bonucci spoke to Milan TV and admitted that the fresh-faced Milan squad were not at their best.
"We must learn from this loss," he said. "Today we saw that if we do not give 100 percent, we can be severely punished by our opponents.
"It's not good, we must improve. We are a new squad. It's my responsibility, and the one of the boss and the management, to lead this group to success.
"Every moment we spend together is important. Tomorrow we'll have time to reflect on today's match, our problem was mostly psychological. It will do us good to take a step back."