We definitely can't blame the conurbation of Manchester for Martial's infidelities. We're all speculating without having firm knowledge of WTF is wrong with him, but at this point I seriously doubt it's down to injuries. What seems most likely, as I write this on my laptop, is that he's never truly been happy at Old Trafford and with not living in France. He started brilliantly, but the manager's tactics didn't allow him to blossom into a worldbeater. Then Jose came and with Jose came a negative mentality and we all know the impact the arrival of Alexis had on Anthony. Anthony enjoyed an uptick in form in the early days of Ole, but when Ole fell apart Anthony never recovered.
We're handcuffed to Martial because of his wages, which no sane club would ever agree to pay, but if somehow possible we should let him go even it meant going on a free transfer.