The skill is there, and he can fill in multiple positions, its more the mind I'd worry about. He's not a mental case, but as
@Sphaero said, he is pretty sensitive. If Mo throws him under the bus he's going to mentally check out. I've met the guy personally, had a conversation with him, comes across very sensible and intelligent, but doesn't handle criticism all that well. Just temper your expectations that you're signing a dependable footballer who can occasionally show moments of brilliance and it should be fine.
Put it this way, if the "what a waste of money" headline Martial endured comes down hard on him, I don't know if he would be able to handle it unless he has lots of positive reinforcement.