Allow me to indulge in just a smidge of fantasy booking here. Lets assume that the injury is legit but that it's only going to keep Punk out for 3-4 weeks and he'll be fit for the Rumble. (We've got to assume that anyway surely, if it was torn ligaments and he was going to be out for 6-9 months, the belt would be off him already). Now, to continue...
The Shield get a flukey win at TLC, when they're celebrating, out comes Punk and Heyman to celebrate with them, followed by.....Vince. They make out like the injury was a work, even though it wasn't. Vince says he wants to protect his most valuable, marketable asset- Punk and his title reign, from Ryback. So Vince, Heyman and Punk contrived this whole injury front, legitimized by a Chairmans letter on the website, to keep Punk away from Ryback. Imagine the heat for Punk- in league with McMahon and messing around the fans?
They can run with it too- Vince goes old school with Punk's match against The Rock and screws Rock out of a win at the Rumble. Think attitude era with Vince and Austin, knocking out refs etc. Vince protects his champion and gets revenge on the Rock for deserting the company etc. Massive pops for the Rock as he opposes them and INCREDIBLE heat for Punk.
If they dared- keep it going til Mania and have him go over either the Rock again or....unthinkably.....Taker. Punk could be the biggest heel in WWE history if he pulled that one off.
Then......imagine the Face pop for the man who eventually takes the belt off him and ends he and Vince's reign of terror?! Ziggler, Orton, Ryback, whoever it is. Their career is made for life.
It's fantasy booking, I know, but it's not that implausible and if done correctly, could work so, so well.