Arsenal are already having some pretty significant injury issues – Kieran Gibbs started today's match against West Brom as a left winger, for the love of God. After about fifteen minutes in the aforementioned game, those problems may have gotten a bit worse.
Francis Coquelin had to leave the match with what looked like a knee injury, after making a sliding attempt to win a 50/50 ball against Claudio Yacob. Coquelin went in slightly awkwardly and after getting the ball, did appear to twist his right knee. He got a few minutes of treatment before signaling to the sideline that he needed to be substituted.
As I said, the injury list is a growing concern for Arsenal, but even if Coquelin does have to miss significant time, Arsenal could conceivably weather it. Mikel Arteta came on to replace him in this game, and one would assume that would be the case for the foreseeable future should it be a long-term injury. Arteta's more than capable, if he can stay healthy, but his past year and a half or so doesn't breed a lot of faith that that's possible. There's also industry mogul Mathieu Flamini, but let's just say I don't trust him as much on the field as I do in a factory.