Pogba, who was skippering the Red Devils, was replaced by Marouane Fellaini.
He pulled up with a hamstring injury after attempting a challenge inside United’s half.
BT Sport commentator Owen Hargreaves said: ”It was a bit of an awkward movement, just stretching. He clutched that hamstring straight away. He’s just over-stretched it.
“If you think about the quality United have in every position, this is the one player who they haven’t really got a replacement for.
“He’s a special player already, he will be the heartbeat of that Manchester United midfielder for a very long time.
“That’s a big blow to Mourinho.”
Fellaini opened the scoring for United with a header from Ashley Young’s cross.
Pogba's injury is a major blow for United, who host Everton in the Premier League on Sunday.
The 24-year-old has been in terrific form for Jose Mourinho this term.
He has two goals and two assists in four league games for the table-toppers.
That form earned him the club’s player of the month award for August.
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