There had been reports over the last few days of Freiburg interest in the Bosnia-Herzegovina international, who turns 27 next month.
Torino and Sampdoria had also shown interest, but MilanNews.it claim the written proposal has now arrived and it is worth €7-8m.
The Rossoneri are likely to give a response over the next few days.
He was purchased from Empoli for €8m last summer, making just 18 competitive appearances for the club.