Arsenal defender Laurent Koscielny lasted less than 15 minutes during Thursday's UEFA Europa League clash before he was substituted with a leg injury.
Per James Olley of the London Evening Standard, the centre-back appeared to suffer the injury after he tried to head the ball:
James OlleyThis doesn't look good for #afc. Koscielny having to come off here just after going up to challenge for a corner. Hard to tell whether its his longstanding Achilles problem or something else.
Calum Chambers replaced the French defender.
Koscielny has been a regular in the Gunners' defence for years and has made 24 starts in the Premier League this season.