The greatest dilemma facing Mourinho surrounds what role Paul Pogba will play against the Hornets. The France international played his first full 90 minutes since returning from two months out with a hamstring injury against Brighton, but could be held back to ensure he is fit for the greater tests which lie ahead.
Michael Carrick is on the road to recovery despite undergoing a heart operation, while both Phil Jones and Eric Bailly – neither of whom have played since the international break - have been training at the United training ground but it remains to be seen whether they will be in contention.
The Manchester Evening News understand that the trio will all miss out, while Marouane Fellaini, Henrikh Mkhitaryan and Luke Shaw have all been omitted from the squad which travelled to London this afternoon.
But Jesse Lingard, Matteo Darmian and Daley Blind have reportedly made the trip and are in contention to feature against a Watford side whose coach Marco Silva continues to impress amid continual links with the vacant managerial position at Everton.
Victory at Newcastle United was Watford's second in a row and sees them occupy a place in the top eight – a full 11 points above the relegation zone – for the visit of United.
Among the highlights of Watford's campaign last term was a 3-1 win over Mourinho men, and another stern test awaits the Premier League title contenders.
"Against Watford I was very upset with Watford's first goal after some guy sent (Anthony) Martial to the hospital and the referee let it go," the United boss said, according to the Evening Standard. "That is the reason why I was very, very upset at Watford. I think Watford made also progress.
"They have an unusual squad for a mid-table team. They have a squad full of very good players who are not normal to be in these mid-table teams. They have a good coach. They have improved a lot from last season too."