The 22-year-old Frenchman is facing punishment from the club for failing to return to the United States for the final week of their five-match tour after he went home to France for the birth of his second child.
Martial’s relationship with manager Jose Mourinho is at an all-time low, and the player wants to leave the club because of his lack of game time.
He started only 18 league matches and missed out on a place in France’s victorious World Cup squad as a result.