CM: Granit Xhaka
Nemanja Matic's injury will be a huge blow for Mourinho - the Serbian has started every match this season, and has been in great form so far.
With Fellaini also out for today's match, the Portuguese boss will have to go with Herrera in holding midfield, but Arsenal's Swiss midfield enforcer has been far better than the Spaniard this season.
He's played every match for the Gunners so far, providing steel in midfield and allowing Aaron Ramsey the freedom to venture further forward. He has three assists, an 84% pass accuracy, and a 75% tackle success rate.
CM: Paul Pogba
Pogba's long absence after an injury picked up in the Champions League left United lacking creativity and a cutting edge in midfield.
His return has been a welcome boost for Mourinho, after a sudden drop in form that led to away defeats against Huddersfield and Chelsea.
With Matic missing in midfield, Pogba will probably have some defensive responsibilities as well, but Jose will be looking to his star man to make the difference going forward.
CAM: Mesut Ozil
Henrikh Mkhitaryan started the season with a bang, but has fizzled out after providing 5 assists in the opening 3 matches. Mata has been decent, but 1 assist and 1 goal in 10 matches is below expectations.
While Ozil continues to fiercely divide the Gunners' fanbase, he put in probably one of his best performances as an Arsenal player against Huddersfield, providing 2 assists and a goal in a sublime 4 minute spell.
The German will probably be as important for Wenger as Pogba is for Mourinho, with star forward Lacazette being ruled out with a groin injury picked up against the Terriers.