Manchester United vs Arsenal: Gunners braced for 'worst news' over Rob Holding injuryManchester United vs Arsenal: Gunners braced for 'worst news' over Rob Holding injury
Holding was taken off on a stretcher and replaced by Stephan Lichtsteiner in the first half following a challenge by Marcus Rashford.
Aaron Ramsey was also substituted with an injury at Old Trafford on Wednesday night, though Emery believes Holding’s problem is the most serious.
"It's the worst news for us today,” Emery said on Holding. “We are going to wait for the doctor but maybe it's a big injury with his knee.
"Aaron Ramsey is a small injury but after these two injuries, every player responded with good commitment and good mentality to keep in the difficult moments our performance in the game."
Holding has featured in each of Arsenal’s Premier League fixtures since mid-September and his absence over a busy Christmas period will frustrate Emery.
One potential replacement for Holding is Laurent Koscielny, who is yet to feature under Emery having suffered an Achilles injury at the tail end of last season.
Koscielny managed 85 minutes of the Arsenal Under-23s’ Checkatrade Trophy win over Portsmouth on Tuesday and could soon return to first-team contention.
"Laurent is very close to playing," Emery said on Wednesday night.
"He played two matches for the Under-23s, the last on Tuesday. We are thinking he will start with us soon.
"I don't know if Saturday [against Huddersfield Town] is a possibility. We are thinking the Europa League against Qarabag [next Thursday] is a possibility."