Tiger Woods has emerged as a major injury doubt for the Ryder Cup after suffering a recurrence of the back problem that has blighted his 2014 season.
The 14-time Major champion was forced to withdraw from the WGC-Bridgestone Invitational before Sunday's final round at Firestone when the injury flared up.
The 38-year-old's place in Tom Watson's US team was already under question due to a lack of action having destroyed his chances of qualifying automatically, and now his troublesome back is another thing threatening to prevent his participation at Gleneagles in September.
Woods is also almost certain to miss the final major of the season - the USPGA Championship at Valhalla this week.
"It happened on the second hole when I hit my second shot," Woods explained to reporters. "I fell back into the bunker, just jarred it. It's been spasming ever since. It's just the whole lower back. I don't know what happened."
When asked about his prospects for Valhalla, the former world number one replied: "I don't know. I'm just trying to get out of here."
Woods has won more Ryder Cup points than any other Americans, apart from Billy Casper and Lanny Wadkins.
