Just after finishing second in the Masters in April, Woods had arthroscopic surgery to repair cartilage damage. He didn't play 18 holes until his dramatic playoff victory in the U.S. Open over the weekend against Rocco Mediate. Reportedly, this new surgery would be to repair his ACL. In addition, it's also being reported that Woods suffered a stress fracture in his left leg two weeks before the U.S. Open.
It is not clear whether the new surgery would also be arthroscopic.
Bottom line, it appears that this new surgery will force Woods to miss the British Open (mid-July) and keep him from defending his PGA Championship title (August).