I posted this in the newbie section, but decided to post it on here as well.
Hi first I would like to say I am a Manchester City fan first time posting here. Only have watched a couple Manchester United games the season including your game against Chelsea. This will be more my observations of the Chelsea game.
I think that you have better players then they are being portrayed of late. I would say what you are most lacking is a top midfield pivot and while yes Pogba will help with that. I think his skills are best shown a little farther forward. It seemed like there was no connection between your defense and attack. It seemed Lukaku and at times Rashford were stranded up top fairly often. Now while I think you are operating without a top pivot this is not entirely the issue because lets face it many teams with players nowhere good as yours have a team that transitions to attack a lot kicker then your's does. Traditionally that rapid killer break has been one of the key facets of a Mourinho team and at the moment it is missing. I am not sure why this is so he has always been great at this.
To me though this is because your team is too stretched. The space between your midfield and forwards is huge. I don't think Lukaku is actually bad at holding up the ball, but you can only hold it up for so long with no support. Often when he received it him and Rashford would be in a 4v2 with support taking even world class players would find such situations difficult.
I am not sure why this is happening. If it it the positions Mourinho is setting up his team in with the forwards either too far up the pitch or all midfielders sitting too deep, Mourinho telling his midfielders to stay back, or maybe the midfielders themselves aren't transitioning fast enough themselves though I find this doubtful with the qualities your players possess. Maybe it really is the lack of a pivot that is holding you back.
Interestingly Manchester United have covered the least distance covered in the league so far:
http://www.mirror.co.uk/sport/football/news/premier-league-total-team-distances-11478064
I think this shows you are playing too stretched. I am not saying be as compact as Manchester City, but I think distance covered shows your team is not moving around enough as a unit. I can't form conclusions why this is happening, but think their is something tactically wrong with the way you are setting up.