Back spasms not only kept Tiger Woods from playing at Riviera, they forced him to withdraw from a media conference on Wednesday.

Woods, the unofficial host of the Genesis Open, said in a statement that, after getting daily treatment over the last four days, he was advised by doctors to limit all activities.

"He flew out here and got to see one of his doctors," Mark Steinberg, Woods' agent at Excel Sports, said on Wednesday.

"Based on the work they did the last couple of days, they advised he just stay horizontal. It's best to listen to the doctors. The ultimate goal is to get out and play."

Woods has not played Riviera, his hometown event, since 2006. When California-based Hyundai Motor America signed on as title sponsor last year, it picked the Tiger Woods Foundation as the chief charitable beneficiary and the tournament's host organization.

Even when back spasms surfaced in Dubai two weeks ago, forcing Woods to withdraw, he still flew to California on Saturday with hopes of taking part in various tournament activities.

Instead, he has stayed in his hotel.

"The hope was the spasms would calm down," Steinberg said. "And they haven't."

It paints a dark future for Woods, at least for the time being.

He already was out of golf for 15 months recovering from three back surgeries, and his return was promising in the Bahamas the first week of December because of the freedom in his swing and the 24 birdies on his scorecard.

But he missed the cut at Torrey Pines, and then Steinberg said the spasms arrived late last Thursday in Dubai after Woods opened with a 77 and stepped gingerly, particularly when climbing out of the bunkers.

Woods said after his opening round there was no pain in his back, even though that didn't look to be the case.

Missing the media conference only fueled speculation about when he might play again.

Steinberg said he was aware it looked bad that Woods was in no shape to sit for 20 minutes and take questions, though he's not sure how much substance a media session would provide.

"It would have gone like many of them have gone the past several weeks - a lot of questions and no answers. It's frustrating for him," Steinberg said. "But he has given full, maximum effort to get back out here."

Woods also withdrew from the Honda Classic next week in Florida. His next most logical chance would be the Arnold Palmer Invitational at Bay Hill, though Steinberg said the conversations he's had with Woods do not involve golf at the moment.

"The goal is to get everything to calm down, have it calm down for a while, continue to get treatment and get back to a place where he's chipping and putting and hitting balls," he said.