WWE.com has reported this morning that John Cena underwent elbow surgery to remove bone chips. He will be out four to six weeks.
I've just been reading that myself.
I have a feeling that Cena will still appear in a non-wrestling capacity, regardless of whether he's injured or not. Hell, Cena's rate of recovery is superhuman. His last "big" injury in 2008 - in where he suffered some kind of neck injury, only forced him out of action for 4 months.
Four to Six weeks? I'd say three, and he'll still make the Hell In A Cell main event.