Laurent Koscielny was able to get fit enough to play 90 minutes against Crystal Palace, avoiding an Achilles problem that had plagued him. But it appears his foot now has something wrong with it, and he may be unavailable for the first leg of Arsenal's Champions League play-in game against Besiktas. While Calum Chambers has impressed so far in his Arsenal career, I'm not encouraged by the idea of a Chambers-Monreal-Debuchy back three -- remember, Kieran Gibbs is also injured -- nor do I particularly want Ignasi Miquel playing in an actual game.
The good news is that Per Mertesacker could be available for an emergency start. According to the Telegraph, he'll make the trip to Turkey with the rest of the team. Arsene Wenger explains:
I planned to bring the Germans back in contention for Everton but, in case of emergency, I will take Mertesacker to Turkey...It's a bit early for him - ideally he would need one more week preparation but he's willing to play, no problem. We are a bit short.
Wenger has spoken in the past about Mertesacker's devotion to fitness and his training plan, and how it meant he could theoretically return earlier than planned. It's only a few days, so hopefully it won't end up turning sour. But honestly, the best scenario would be a miraculous recovery for Koscielny (again).