IRVINE, Calif. — Tiger Woods is no longer on crutches since surgery last week on his left knee, but he said Friday in his monthly newsletter that he does not know when he will return.

"I knew a couple of months ago I was going to have the surgery," Woods said. "The knee has been bugging me for a while. The only decision was do you miss the Masters or play in the Masters? I decided to play. Even if I had won, I still would have had the surgery."

Woods had arthroscopic surgery April 15, two days after he finished three shots behind Trevor Immelman in the Masters. It was the second time in five years Woods had surgery on his left knee, this time to clean out some cartilage.

He used crutches last week in Las Vegas at "Tiger Jam XI," a charity concert that raised more than $1.5 million for his foundation, and now is in a knee brace. He said he hopes to start rehabilitation soon.

"Needless to say, I'm a little stir crazy," Woods said. "Although I've been through this before and understand the need for patience, I don't enjoy sitting around. I really don't have a timetable for returning to competition. The doctors have said I should be able to play again in four to six weeks, but nothing is certain. I'm just going to do what they tell me to do."

Woods will not defend his title next week at the Wachovia Championship, and he also will miss The Players Championship for the first time in his career. His hope was to return for the Memorial, which starts May 29.

The U.S. Open will be June 12-15 at Torrey Pines, a course where Woods has won six times as a pro.