Martial was said to have rejected a previous contract offer from the Red Devils in October. That bid was reportedly made by United's brass despite former manager Jose Mourinho looking to sell the French international.
As talks between the club and player continued on a new long-term deal, United found an interim solution in December, triggering a clause in his contract that extended Martial's stay at Old Trafford until 2020.
Martial joined United in 2015, moving from Monaco as a 19-year-old in a deal reportedly worth up to £58.8 million, and has since scored 45 goals in 159 appearances over four seasons in England. He's currently tied with Romelu Lukaku as United's top scorer in the Premier League this season with eight goals each, though Martial has reached the mark in two fewer appearances.