This was his third tournament back on a Firestone Country Club course where he has won eight times. He opened the tournament with a 68 but got progressively worse and was 3-over par for his round when he withdrew Sunday.
"It's just the whole lower back, I don't know what happened," he said.
Woods' status for the PGA Championship this week in Louisville, in which he is scheduled to play, is unclear.
"I don't know," he said. "Just trying to get out of here."
Phil Mickelson, who is scheduled to play with Woods in the first two rounds of the PGA Championship, saw Woods struggling on the ninth hole while he was playing the 11th.
"It didn't look good," Mickelson said. "It looked like he was really in pain. I hope he's OK. I mean, I hope he's able to play next week. I hope it's a muscle and nothing serious because I'm really looking forward to playing with him. We rarely get paired together. If we do, it's been early Saturday.
"So it's nice to be paired together and have a couple of rounds and I hope he's able to play it. As much as I love playing with him, playing against him, trying to beat him, it's we all want him in the field. We all want him back. I just hope he's OK."