After helping PSG to the an unprecedented Quadruple last season, which included the Champions League title, Donnarumma was sold to City this week.
His former coach at Milan, Magni, has slammed PSG and coach Luis Enrique for pushing the Italy No1 out of the club.
He told Eurosport: "Beyond the contractual issue, I can't believe PSG's decision was purely a technical one. There's no question about Gigio. I can say this and guarantee it: Gianluigi has the talent to do what Luis Enrique asks. It's normal for a coach today to ask goalkeepers to play much more with their feet; football has evolved.
"Just as it's normal, for example, to demand deep-lying coverage that adapts to different phases of play. But how is it possible that what Luis Enrique criticizes Gianluigi for is okay with Pep Guardiola? I ask myself this question.
"I repeat: Donnarumma has all the talent necessary to meet any coach's expectations, provided he's put in the right conditions. If Luis Enrique thought he didn't have the required characteristics, Gianluigi still had the ability to meet them. If Luis Enrique criticizes him, for example, for not knowing how to play the ball and for making poor team decisions, I can guarantee that Gianluigi can do it.
"He knows the game; he's had many coaches and trainers. If he's not able to pass the ball quickly over medium or long distances to create numerical superiority in a certain amount of time, you work on it. You strengthen your ankles and things will go better. He has the ability to respond to any request; I don't understand why he continues to receive such criticism.
"And regarding the criticism leveled at Gigio , he continues: "I can't understand what they're criticizing him for. I think he's very good at making decisions. And I know Gianluigi; he can listen to everything, take it in, and make adjustments. I don't know exactly what Luis Enrique was asking of him, but I refuse to believe his departure is due to a technical issue. For me, the reasons go beyond the sporting aspect."