Romelu Lukaku was forced off with a head injury only eight minutes into Manchester United's Premier League meeting with Southampton on Saturday.
Shortly after heading over with United's first chance of the match at Old Trafford, the Belgian striker was involved in a clash of heads with Saints defender Wesley Hoedt.
Lukaku, who appeared to be in some discomfort, received treatment on the pitch for several minutes before being stretchered off, with Marcus Rashford coming on in his place.
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The severity of the injury is unclear, but Lukaku could now be in doubt for a return to former club Everton on New Year's Day.