Loftus-Cheek was taken from the pitch on a stretcher after being injured while attempting to meet a cross around the 10-minute mark at the San Siro. Milan lost the match 1-0.
"In addition to broken upper teeth and two cuts, the Englishman suffered a fractured alveolar bone," Sky Sports Italia reported. "This is a very serious injury; he will undergo surgery on Monday ... and is expected to be out for several months."
AC Milan did not immediately respond to a request for comment outside normal business hours in Italy.