The centre-back injured his groin and was replaced by Kieran Gibbs just four minutes into the game.
Arsenal manager Arsene Wenger revealed after the game the extent of the injury, which looks to be short-term setback for the 27-year-old.
“He has a groin strain. That's usually three weeks," said his manager. Arsenal have had the luxury so far this season of all their four first-team regular central defenders available for selection – Per Mertesacker, captain Thomas Vermaelen, alongside the Frenchman have kept fourth-choice centre-back Johan Djourou out of the team for the entire season.
The Swiss international has featured in just one Capital One Cup game for Arsenal this season; such has the fitness and relative form of his competition. The skipper has been perhaps the underachiever of the three – his performances in Arsenal’s backline have been inconsistent and, in general, under par for the Belgian.
Giant German Mertesacker has looked to have improved via his first tough season in the Premier League – he is still, however, prone to being caught out of position and his lack of pace remains a concern for the North Londoners.
Koscielny has been the best of the three overall – he’s learned how to stay of his feet, he’s fast, he stands up well in aerial duels and he’s developing his reading of game. He’s even tried not to score that many own-goals, with some success.
It’s unlikely that Wenger will have cause for major concern – three weeks is nothing to panic about – but the major issue will now be his restriction on squad-rotation which, going into December, as the games come thick and fast, is not an ideal time to have your best defender injured.
Should either Mertesacker or the skipper pick up a knock, a niggle or a red card, Wenger would have no option but to cover the absence with a player who has played one game in more than three months in Djourou.
They’ll be without the Frenchman for their weekend clash with Swansea City, along with at least four more Premier League fixtures, their final Champions League group game next week, and their quarter final of the League Cup against Bradford.
They’ll be hoping he makes a swift recovery in time for the New Year. January brings them season-defining games against Manchester City, Liverpool, and Chelsea. Until then, they’ve probably got enough to go around.
The good news is Gibbs is back healthy. With Koscielny in the middle Vermaelen has been able to play at left-back, but he won't be able to do this with Koscielny out. Nor will he need to, for now, but if Gibbs gets injured again, you know what that means... Andre Santos.
image: © Ronnie Macdonald