The Italian champions saw Dalot up close and personal during a loan spell a couple of years ago.
However, the move was not made permanent, and he has since established himself in United's first team under Erik ten Hag.
According to Calciomercato, Milan are not happy with Sergino Dest's displays so far this term.
The 23-year-old is not likely to be long for the club, which means they are looking to sign a replacement in January or the summer.
Dalot's name has entered their thinking, especially if he has not agreed a new contract with United by the end of this season.