The immediate and long-term future of Tiger Woods is in serious doubt after the former world number one withdrew from the WGC-Bridgestone Invitational during Sunday's final round.
Playing just his third event since undergoing microdiscectomy surgery on March 31, Woods had completed his opening eight holes in three over par when he pulled out on the ninth hole at Firestone Country Club.
Woods looked in severe pain from his back after hitting his tee shot on the 494-yard par four, wincing as he struggled to bend down to pick up his tee.
And minutes later he was on a golf cart being driven straight to the car park, where he again looked in real discomfort as he prepared to leave a venue where he has won eight times, including by seven shots last year.
Asked if he had suffered the same injury which led to the operation which ruled him out of the Masters and US Open, Woods told reporters: "It's just the whole lower back. It happened on the second hole when I hit my second shot. I fell back into the bunker. Just jarred it. It's been spasming ever since."
On his prospects of playing in this week's US PGA Championship at Valhalla - where he beat Bob May in a play-off in 2000 - the 38-year-old added: "I don't know, (I'm) just trying to get out of here."
Woods then gingerly made his way to the passenger side of his courtesy car before being driven away by caddie Joe LaCava. His agent Mark Steinberg was later quoted by the Golf Channel as saying Woods had flown home to Florida for evaluation and that a decision on playing in the US PGA would be made "when ready."
The 14-time major winner had made the ideal start to his round with a birdie on the first, but mis-hit his approach to the third into water, saved par on the fifth despite his tee shot coming up 60 yards short of the green, bogeyed the sixth and then ran up a double-bogey on the seventh.
European Ryder Cup captain Paul McGinley, commentating on Sky Sports 4, said: "He looks like he's maybe come back too early. The way he played, I saw him hit shots on the front nine there that I've never seen him in his life come close to hitting. There's obviously something going on."
Woods missed the cut in his first event back at the end of June and then suffered his worst ever 72-hole finish in a major championship as a professional, ending up 69th in the Open at Royal Liverpool despite an opening 69.
He had previously spoken about being "pain-free" for the first time in two years, but said on Wednesday that other people who had undergone the same surgery "had no idea" how he was able to play again so quickly.