Woods was 5 over for the final round, 12 shots behind Rory McIlroy, when he shook hands with Luke Guthrie on the 13th green. The tournament sent a van to collect Woods and his family, and police kept media from the parking lot.
"He just came over and said, 'I can't go anymore. It was a pleasure playing with you,'" said Luke Guthrie, paired with Woods the last two days. "I just said, 'Take it easy. Feel better.' Pretty uneventful."
Woods said through spokesman Glenn Greenspan it was lower back problems that started Sunday morning as he was warming up.
He was to defend his title next week in the Cadillac Championship.
"Too early to tell," Woods said in a statement about playing next week at Doral. "I'll get every day to try to calm it down. Just don't know yet. Wait until Thursday and see how it feels."
Woods already has played a limited schedule this year — 10 rounds at portions of four tournaments. He was to play twice more before the Masters on April 10-13.
Woods said the spasms were similar to what he felt last August at The Barclays, where he dropped to his knees after hitting one shot. Woods finished that tournament in a tie for second, one shot behind Adam Scott.
It was the second time in two years that Woods has walked off the course in the middle of the final round. He quit after 11 holes at Doral when he was well out of contention — and then won Bay Hill two weeks later for his first PGA Tour title since his return from the chaos in his personal life.
Woods had said earlier this year in Dubai that he spent the majority of his offseason working on his physical strength, at the expense of neglecting his game. He opened the year by missing the 54-hole cut at Torrey Pines (where he is an eight-time winner), and then tying for 41st in the Dubai Desert Classic.
Two years ago at Doral, Woods was driven in a cart to the parking lot, and NBC Sports showed footage of his Mercedes-Benz driving out of the Miami resort toward his home about an hour north in Jupiter.
This time, police blocked the media from entering the players' parking lot. Woods was seen getting out of a white passenger van with his mother and other members of his group.
It was the second time the No. 1 player in the world walked out in the middle of the Honda Classic. A year ago, McIlroy quit after 26 holes because of what he said was a sore wisdom tooth. He later said the frustration of a poor start to the year got the best of him.
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