He is struggled a little after injury (limited defensivly and ball hogs at times), so people forget he us basically most important player this season in terms of creativity and pattern breaking mobility in this Motta system.
Keep him in mid season for sure to ensure best possible outcome for this season, which is CL spot that will make or break our near future.
Only exception to that if City makes a fuck it offer. And 50m isn't that imo. 70-80m is tho for a fullback, who is good a little above mid level talent wise. So that would be huge offer for him.
If that doesn't come don't even entertain the idea of losing him mid season imo. Harder to replace now. He is more important to us tactically (false back role key for Motta with his conservative use of FBs)then anything he can offer them now.
If we revisit this in summer where you can have more time to replace, then it's another matter.