#3 Manchester United's injury crisis
The current Manchester United team is not the same team that managed four 4-0 wins in their first 6 matches of the season. With the likes of Pogba, Fellaini and Carrick missing, United have lacked the depth needed to consistently perform at the three competitions they are currently a part of.
Ander Herrera and Nemanja Matic have been the combination of choice in midfield and have been playing every week. As a result, the midfield engine is open to fatigue and coach Jose Mourinho does not have any other experienced midfield players at his disposal to use as substitutes.
As with any Mourinho team, there need to be enough options on the field, as well as on the bench to help him cope with any changes in tactics during the game. Without a full bench, Mourinho has been known to withdraw into a shell and look towards playing a draw instead of marching full-steam ahead.
Without his full team, the only option left with Mourinho is to play deep and wait for an error on Chelsea’s part to strike on the counter-attack. Though the tactic has worked previously for Mourinho, it also erodes away at the attacking discipline of the team as seen in the last few matches. Additionally, sitting deep seems like a last-ditch effort and any mistake in defence can land them in a hot mess.