The French international has had surgery on a dislocated shoulder.
Arsenal have not exactly had the best of luck with injuries this season. In fact, when do they ever?
Today's injury update from Arsene Wenger to Arsenal.com certainly did not read cheerfully.
Of course he first had to confirm that Mikel Arteta was set to miss around three more months of action with his ankle problem. The Spanish midfielder underwent surgery on the problem this week and is now on the track to recovery.
At the weekend Arsenal took on Stoke City and were comfortable 3-0 winners. But it was not a comfortable afternoon for Mathieu Debuchy. The French international was bundled into the advertising boards by Marko Arnautovic and dislocated his right shoulder.
Wenger gave an update on that injury and it would appear that Arsenal will be without Debuchy until April:
"Mathieu had a surgery on his right shoulder following the injury on Sunday. It's very unfortunate for Mathieu, it's unbelievable because he's had two surgeries in the same season. He just came back, he played seven games and he's out again. I count three months out for Mathieu because contact will be a problem for the shoulder."
It means Calum Chambers is likely to return from illness just in time to replace the former Newcastle man at right-back for the side. If not, young Spaniard Hector Bellerin is another option.
As for Kieran Gibbs' heel injury and Danny Welbeck's thigh complaint it is mixed news. The left-back appears to be a maybe and the striker is definitely out for the game with Manchester City this weekend:
"Kieran Gibbs will be training again with the squad on Friday and we will see how he goes from there. His news is positive.
"Danny Welbeck is not ready yet, he is still feeling some pain, so we will have to be patient."
All in all, not great news from the Arsenal medical department this afternoon.