My five cents is that our tactical shape is pretty terrible. We keep putting the ball on Martinelli on the left flank even though there's nowhere for him to go. He looks low on confidence right now and I don't think you can blame him, it's a thankless job. Opponents know it's coming and he's always marked. The whole point is to let other players move up before we try to attack. It's slow and inefficient but means you're less prone to getting caught on a counter when you lose the ball.
You saw this with Ødegaard yesterday too. Bloke could open a tin of beans with either foot but he can't play a simple forward pass when he has two runners in front of him? Get real. He held the ball because that's the instruction. We don't go direct. We use the left flank to stretch the field. He was waiting for the run on the left that never came. I was watching clips from last season and he did exactly the same thing there. Then he goes home to Norway for an international break and slices up opponents for Haaland like he's prime Fabregas.
Arteta needs to change this or it won't matter much who plays left wing. Maybe United away isn't the right game to experiment too much in, but our shape is hampering the attack.