Back in the summer I was one of the few who were against signing him. I just didn't think he was what we needed. After a disappointing start to his United career, when he was brought back into the squad and put together a string of impressive performances I admitted I may have been wrong about him. Lately, he's playing like the Mkhi I didn't want here, though I still like him and think/hope he has a place here.
I don't even think he's been that bad recently, and he was by no means a bad player at Dortmund; I'm just not sure he suits the PL/José. I never saw him as a particularly good dribbler or shielder of the ball (he gets dispossessed too easily). Anyway, I actually thought his general play against Celta was good, and I thought he did well today considering he was pretty much a LWB. No point judging his City performance as the tactics were just bad from José and limited him, Martial and Rashford.
I think if he isn't burdened with a whole lot of defensive duties (not playing as a LWB!) and was allowed a bit more freedom, he may begin to blossom again. I'm not saying have him do no defending, just not to the extreme levels of having him be pretty much a defender.