United begin the week eight points adrift of Arsenal, while there are just two points separating the North-West outfit to 10th-placed Watford.
Mourinho is likely to make changes for the visit of the Gunners, and here Sports Mole looks at how his team could line up at Old Trafford.
Out: Alexis Sanchez (thigh), Victor Lindelof (thigh), Ashley Young (suspension)
Doubtful: Chris Smalling (ankle), Eric Bailly (back), Marcus Rashford (fatigue), Luke Shaw (knock), Antonio Valencia (knock)
United will be without Ashley Young due to a one-game suspension, and that could lead to Diogo Dalot getting an opportunity at right-back.
Chris Smalling missed the trip to St Mary's at the weekend, but the defender could return to the centre of the backline with Scott McTominay the player to miss out.
Luke Shaw is being assessed after sustaining a knock at the weekend, while Marcus Rashford could drop down to the bench after it was suggested that the England international was suffering with fatigue.