Manchester United will be without strikers Romelu Lukaku and Zlatan Ibrahimovic after the duo picked up injuries.
The Belgium international banged heads with Saints defender Wesley Hoedt in the ninth minute of the Old Trafford contest.
Lukaku stayed on the ground after the incident and was tended to by medical staff for fully five minutes before he was carried off, to a standing ovation.
He will miss Monday’s game against Everton at the very least, as FA rules state a player who suffers suspected concussion cannot return to action within six days.
Manager Jose Mourinho also says Zlatan Ibrahimovic will be on the sidelines for a month.
The 36-year-old forward did not feature at all during United’s 0-0 draw with Southampton on Saturday evening, having been taken off at half-time during the midweek clash with Burnley.