There's something just not right with him. I mean for so many players, when your form is that bad, they might try and work even harder to compensate for the lack of output. Rooney used to go through barren spells, but run himself into the ground all the same.
Martial is not only a shadow of the player he was last season, his effort is completely terrible. Now any player can go through a bad run of form, but not trying is just unforgivable. It's not the lack of goals or assists, it's the lack of....well, anything.
Drop him, and if there's not a reaction then sell. Talent is nothing without the mentality to go with it. I can barely stand to see him on the pitch these days.