Tiger Woods was forced to withdraw from the WGC-Bridgestone Invitational during the final round with a back problem that could threaten his participation in next month's Ryder Cup.
Woods, 38, was playing in just his third event since undergoing back surgery in March which ruled him out of action for three months.
The 14-time major winner looked to be in pain after hitting a shot on the edge of the bunker on the second hole, round four, at Akron. Later he missed the fairway with his tee shot on the ninth before leaving the course.
Woods, an eight-time winner at the Firestone Country Club, was unable to continue, immediately casting doubt over his participation in the final major of the year at the USPGA Championship this week and possibly at Gleneagles in September.
"It's just the whole lower back," Woods said of the injury.
"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."
When asked of his chances of taking part at Valhalla this week he said: "I don't know, I'm just trying to get out of here."
Woods returned to action three weeks ahead of his own schedule at the Congressional in June following a three-month absence where he missed the cut by four shots.
The former world number one was also in action at the Open at Royal Liverpool in July where he finished the weekend six over, but with no reported back troubles.