CM Punk has been injured for several weeks now, which is why he's barely been wrestling a full match at recent WWE live events. Word is that Punk's knee and ankle are injured but he's dealing with other nagging injuries. The attack from Ryback at Night of Champions will allow Punk one or two weeks off TV. 

Other sources reports that a lot of people within WWE are talking about how Punk's deal expires next summer and what that means for his future. It's probably too early to tell what's in store for him but it is something being talked about among the other wrestlers.