As reported by wwe.com :

WWE.com has confirmed that Dr. Andrews completed a scope of CM Punk’s left knee. Andrews successfully trimmed a cartilage tear in Punk’s knee.

“CM Punk underwent knee surgery today to remove a piece of torn meniscus that had locked up his knee,” said Andrews’ colleague, WWE physician Dr. Chris Amann. “The surgery, performed by Dr. James Andrews, went smoothly and CM Punk is expected to make a full recovery.”

This puts Punk's status for the upcoming TLC PPV which is just 12 days away in jeopardy.