Article doesn't specify the injury at all, which I interpret as a good sign; pretty much indicates that he just fell hard is all, and they kept him out as a precaution.
Thank God dude; we definitely need his experience and veteran presence for the playoff run. McCourty is shinning now that he can just focus on his game more, and Talib at least was able to bring Andre Johnson back down to Earth, after that monster month of November he just had. I wouldn't mind him just sitting out the SF game all together, if need be. That is a likely Superbowl opponent though, so my guess if he's good to go by Sunday, precautions will take a back seat.