Just watched the full match again and maybe I was harsh on him when watching it live.
He did make 3 or 4 obvious errors, but he also did a lot of good things, and had more of a mixed game rather than an absolute stinker.
He made a couple of great chances for other players, had a couple of really good balls superbly intercepted by defenders, made some good runs back to intercept and win free kicks. He did actually help the team and contribute.
Most of the obvious errors all came in a short period of time though, and it's even more frustrating when you know they're one of the most talented players on the pitch.
It does look like he's slowed down a little, and I agree with some of the posters above that he may prosper more playing closer to Lukaku and coming in from the right. Worth trying and would leave that left hand side open to Rashford and Martial to fight for again.