The midfielder missed out on the Red Devils’ first Premier League match of the season due to a suspension carried over from his time at Juventus and a lack of pre-season training had cast doubt on his involvement at St Mary’s.
Mourinho revealed, however, that the Frenchman is nearing full fitness and is likely to feature against the Saints.
“We played against Leicester with players with less training than him and we saw that match as a way to improve them and accelerate the process,” the Portuguese told MUTV.
“With Paul it’s a bit the same – he hasn’t played in one single minute of any pre-season matches but has done almost two weeks of work with us, sometimes with the group, sometimes separately, and he is okay now to play some minutes.”
The Red Devils also have Chris Smalling, who sat out the season opener due to a red card he picked up in the FA Cup final, available for the Friday night clash, while Jesse Lingard has recovered from an injury suffered in the Community Shield.
Jose Fonte, who has been linked with a move to United, is in contention to make his first start of the season for Southampton after being given extra holiday following Euro 2016 but Ryan Bertrand is injured.
- Manchester United have failed to win any of their last three home Premier League games against Southampton (D1 L2) after a run of 13 wins in 14 games against them before that.
- Southampton have won their last two league trips to Old Trafford, both 1-0; they have never won three in a row there in their entire league history.
- Manchester City are the only side to win three consecutive Premier League away games against Manchester United at Old Trafford (between 2011 and 2014).