Martial upset the United manager, by leaving the team base in Los Angeles last month against his wishes and flying to Paris to be with his partner, Melanie Da Cruz.
The unsettled French winger angered Mourinho further, by refusing to return to America after the birth of baby Swan.
It is understood that Martial has been fined £180,000, the equivalent of two weeks’ wages.
The Portuguese coach revealed Martial’s punishment when responding to comments from Paul Pogba, that he would be fined if he discussed his situation at Old Trafford.
“I don’t care. You have to ask Paul (Pogba). I’m here for two years and a couple of months, and the only player that was fined was Anthony Martial. So it’s not easy to be fined here,” Mourinho told reporters on Friday, ahead of their Premier League clash at Brighton.