World number one Jason Day withdrew from the final round of the BMW Championship on Sunday due to a back injury.
Day, who is already guaranteed a place in the season-ending Tour Championship - starting on September 22 - and remains in with a chance of winning the FedEx Cup, has a history of back trouble.
The Australian was defending his title at Crooked Stick this week, but opted to leave the course after completing eight holes of his fourth round.
He was two over for the day and three under for the tournament - well adrift of leader Dustin Johnson - when he brought his participation to a premature close.
A tweet from the PGA Tour's official media account confirmed the reason for Day's withdrawal.
It read: ".@JDayGolf WD from @BMWchamps during R4 with a back injury. @PGATOUR."