Arsenal are short at the back after the French full-back was injured against Manchester City.
Arsenal will take plenty of positives from their 2-2 draw with Manchester City at the Emirates Stadium on Saturday, but the biggest concern could be the sight of Mathieu Debuchy being stretchered off late in the second half.
The right-back, who joined the club from Newcastle United in the summer, went down clutching his knee after stretching for an innocuous bouncing ball and was given oxygen before being rushed to hospital.
The issue is not with his replacement. Calum Chambers, another summer signing, has been excellent since he joined the club and is a natural fit having played at right-back for the majority of his young career.
The lack of depth in the centre of defence, however, could now be a major problem as Arsenal look to challenge for the Premier League title.
With Chambers on the right, the Gunners are completely devoid of options in the middle, aside from the pairing of Laurent Koscielny and Per Mertesacker.
The duo are tried-and-tested Premier League defenders, but they will now be relied upon to play every game in the Premier League, Champions League and domestic cup competitions.
Any injury to Koscielny, Mertesacker or Chambers would leave the Gunners desperately short at the back. Young full-back Hector Bellerin could be handed an opportunity, but he is so far unproven a the top level.
Wenger's failure to address Arsenal's lack of depth at the back, however, looks to be a real oversight with Debuchy going down so soon after the transfer window closed.
After the sale of Thomas Vermaelen to Barcelona, the Arsenal manager should have looked to beef up his backline with at least one player capable of playing at the heart of defence.
The Gunners will now need some luck if they are to make it through to January without a real crisis in defence, particularly when the fixtures start to come thick and fast later in the campaign.
There is pressure on their two central defenders to play well consistently and to stay fit with no depth behind them, but with just one or two more summer signings Wenger could have avoided this situation.