The Italian defender joined Milan last summer amid a raft of new signings as they set their sights on a tilt at the Serie A title.
But they finished sixth last season and face having to sell their assets due to FFP regulations.
Yahoo Sport reports United are keeping tabs on Bonucci’s situation with Jose Mourinho keen to strengthen his backline again this summer.
Bonucci is 31 now but would offer some incredible experience to the United defence.
