"All other tests carried out by the squad and staff came back negative," it added. "Training ahead of the match with Napoli will resume on Monday, subject to the checks set out in the (Italian federation) protocol."
A number of Milan's squad are currently away with their respective national teams during the international break.
Several Milan players have previously tested positive and subsequently recovered including goalkeeper Gianluca Donnarumma and forward Zlatan Ibrahimovic.
Still unbeaten in the league, Milan lead with 17 points from seven games and face Napoli on Nov 22.