The Arsenal website has officially announced that Mathieu Debuchy is leaving the club, in a loan deal with Bordeaux until the end of the season. Debuchy hadn't been having a happy season so far – he wasn't getting a lot of playing time, and when he did he looked like death warmed over. A trip to France should hopefully solve both issues for him.
The question is, of course, what happens now at the right back position. The first answer is "everyone hopes that Hector Bellerin can handle playing every week all season," though we were already working on finding out whether or not he could so not much changes there. In terms of backup for Bellerin, second chair probably now falls to Calum Chambers, who's also our backup defensive midfielder and center back. Francis Coquelin can also play there, and Mathieu Flamini played fullback in a Champions League semifinal once so that's a thing.
In the longer term, whether Carl Jenkinson or a new signing replaces him (or hell, a youth player?) it seems very unlikely that Debuchy will return to Arsenal. Stranger things have happened, but the #2 shirt is probably about to be available again. Godspeed, Mathieu. You were fine until you weren't anymore.