Krunic, 26, joined Milan from Empoli last summer for a reported fee of €8m plus bonuses.
He has been used rarely by Milan though, starting in just four of his 15 appearances in the latest Serie A season.
And according to TMW, the 13-time Bosnian international could be heading to the Bundesliga.
Freiburg have taken information about Krunic and are working on a deal, but his salary is an obstacle.
Torino are monitoring developments and could enter the bidding if Freiburg fail in their pursuit of Krunic.