The rumour circulating is that Bayer director of sport Rudi Völler has flown to Milan for advanced negotiations.
A deal was struck quickly, according to reports, handing over the very promising centre-back for €3m.
Donati grew up through the Inter youth academy and had been on loan in Serie B with Grosseto this season.
He turned 23 in February and can play centre-back or right-back.
Donati was among the most impressive in the Italy Under-21 side that reached the European Championship final.
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