Donnarumma was reduced to tears in the dressing room and had to be comforted by defender Leonardo Bonucci after banners were unfurled describing the 18-year-old as a "piece of sh**" and reading: "Under duress is earning €6m per year and paying the wages of a parasitic brother? Leave now, we're out of patience".
The fan reaction came after reports that the player's agent Mino Raiola was attempting to have Donnarumma's contract extension 'annulled' on the grounds that he was pressured into signing it.
Speakign following the 3-0 victory, AC Milan manager Gennaro Gattuso defended his goalkeeper, pledging to offer him "all the protection I can give."
"He's an 18-year-old kid, of course he was shaken. I can only thank him for what he's doing," Gattuso said.
"For his age, he's the best goalkeeper in the world right now. You can tell from his face he's not happy, but I have known a great athlete and great kid. He will have my protection, for all the protection I can give.
"If the club says it doesn't need to sell anyone, nor wants to, then why should we even talk about this?
"I respect the fans, but he sulked at me for four days because I left him at home for the first time in seven months. He never skipped a training session, let alone a game.
"People need to understand whether Gigio really does want to go or if he wants to stay. I can say I'm working with a great athlete and professional.
"I am the coach of Milan, so I can talk about the lad, the athlete, but nothing else. Gigio has not told me personally that he wants to leave. If he did, that would be different."