Disclaimer:
Shameless conspiracy theory incoming from a Martial FC highest security level card holder:
Martial is not injury prone at all. We are skint and can't pay the appearance-per-season related add ons attached to his purchase which actually take his price up to £58M and will cause us to fall foul of FFP. The "board" have thus installed a stooge in the medical department to assign a random injury to him whenever there's a danger that he hits any of those milestones.
Ronaldo was the initial solution to prevent Martial performances (which is why the club strangely refused to let him leave earlier), but it became obvious quite quickly that he was an insufficient solution.
EtH needs him for the run-in and has agreed with the board that they should pull their stooge if he's within 5 points of the league leaders with 10 games to go. (10 + whatever his appearance record is now = just below the threshold)
Martial being the consummate, unselfish professional and company man on his part has grudgingly agreed to this.