The Italy international is reportedly on the radar of an array of top European clubs after announcing his intention to let his deal run into its final year.
Milan were widely expected to cash in on the in-demand stopper, who has 71 first-team appearances under his belt despite being just 18 years old, but Mirabelli has suggested that he will not be allowed to leave.
"Donnarumma is a great champion, a great guy and a Milan player," he told Sportitalia. "For this next season, he will certainly play with us still.
"It's the coach who makes the decisions. They say who will make the bench or sit in the stands - it is not in heaven or on earth. This applies to everyone - not only for Donnarumma, but also for the other players and those who will come."
Donnarumma featured in all 38 of Milan's league games last season, while also appearing a further three times in other competitions.