Mourinho is yet to have all of his squad fully fit and available because of injury and post-World Cup breaks, with Alexis Sánchez, Nemanja Matic and Antonio Valencia among the senior absentees on Sunday.
On United's pre-season tour the Portuguese pointed to the opening two matches as problematic due to the number of players missing because of holidays taken after Russia 2018.
United's next game is at home to Tottenham Hotspur next Monday, so Mourinho will have had more than a week to prepare for a match where he will be under pressure to record a win.
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