The 22-year-old was involved in a big collision during the first-half of the Europa League defeat against Feyenoord on Thursday night.
However, he was treated on the pitch and despite limping for several minutes afterwards, was able to complete the match.
Bailly is set to be assessed by United’s medical staff at Carrington on Friday before Mourinho makes a decision based on whether he will be fit enough to start.
He has been on of our best performers of the season so far and is the only player along with David de Gea who has played every minute of the new campaign.
Daley Blind did make the trip but was not named in the squad and should return against Watford, if Bailly is injured we could see a Smalling and Blind partnership for the first time this season.
Hopes are the injury with Bailly is nothing serious, he’s been one of our best players so far and losing his presence on the pitch would be a massive blow for Mourinho’s side.