Mesut has a problem with his foot, an inflammation, but it's very short term - very short term. He'll be back next week.
That's good news, because with Özil absent in today's match, the Arsenal attack was nowhere near as potent as it's been for much of this season. It's also good news because "next week" Chelsea comes to visit the Emirates Stadium, and even in their current somewhat weakened state it'd be nice to be as close to having all hands on deck as possible.
As for the Chilean forward, Wenger says he could have played today in theory but it wasn't a risk he was willing to take.
Because he was at 95 percent there, but with a muscular problem I didn’t want to take a gamble because if he has a setback now it’s three months. I think he’s a few days away so it was not worth the gamble.
If Alexis truly is only a few days away, it's possible that he also will return to face Chelsea. It really would be nice to have him back, too – while Joel Campbell has shone brightly after being given a chance, this Arsenal strike force could definitely use more of Alexis' magic.