There are some definite weaknesses in his play which I think are more mental than physical and are the kind of things that you're either born with or not. He lacks basic aggression for one, similar to Lukaku. He might not be a mountain of a lad but he's still a decent size to be getting across a defender and making himself a nuisance by throwing in a forearm or backing in. Whether this can be taught by being a little cuter to win a cheap free kick to compensate I don't know but some games you hardly know he's playing for about 20 minute stints. May just be inexpereicne
He's got potential and hopefully with a manager to focus on him and maybe Rooney taking him under his wing he can improve but he'd greatly benefit from a bit of support from January onwards so he can continue to grow out of the team for periods.