WWE posted the following on their website:
WWE Chairman Mr. McMahon has released a statement through his office, speaking to the developing situation surrounding the WWE TLC pay-per-view. Because of the previously reported knee injury to WWE Champion CM Punk , suffered this past Monday night on Raw , Punk is unable to compete at WWE TLC against Ryback Sunday, Dec. 16.
In the statement, Mr. McMahon also announced that a Six-Man Tables, Ladders and Chairs Match has been added to the pay-per-view, in which Ryback will team up with WWE Tag Team Champions Team Hell No to battle The Shield. Furthermore, for the first time ever, the winner of this TLC Match will be determined via pinfall or submission.