The Red Devils opted for both Nemanja Matic and Scott McTominay in midfield at Old Trafford, and Mourinho has since revealed that Pogba's absence has come after the 24-year-old picked up a knock during training on Friday.
"He's injured," Mourinho told Sky Sports News before the game. "Yesterday in training. He was in an unlucky situation. I don't know how long he is out for."
The French playmaker has been in and out of Mourinho's side of late following ongoing reports of tension between the midfielder and the Portuguese coach.
Pogba is spending his second season at United after rejoining from Juventus for £90m in the summer of 2016.