Arsenal's superb 2-0 win over Chelsea on Saturday night was tainted as full-back Hector Bellerin was stretchered off with a knee injury.
First-half goals from Alexandre Lacazette and Laurent Koscielny gave the Gunners victory, and put them back within three points of the top four.
However, they lost Bellerin after 72 minutes after he went down without contact from a Chelsea player, appearing to twist his knee.
Another injury would be a cruel blow to the 23-year-old, who only returned from a calf strain in the defeat to West Ham last weekend, and was making his first Premier League start since the loss against Southampton on December 16.
"It is his knee," Emery confirmed after the game.
"The first prediction is it is an important [bad] injury. I hope no, but it is not positive, our first impression."
Ainsley Maitland-Niles deputised at right-back for the final 20 minutes at the Emirates, while Unai Emery could also use Stefan Lichtsteiner or Carl Jenskinson in the position, if Bellerin's injury turns out to be serious.
Arsenal’s next fixture is Friday night’s FA Cup fourth-round clash with Manchester United at the Emirates.
