CARMEL, Ind. – World No.1 and defending BMW Championship winner Jason Day was forced to withdraw with a back injury through just eight holes of the final round, putting his place in the Tour Championship under a cloud.

Day tweaked his lower back when he bent down to put a tee in the ground on the ninth tee box and decided to pull out of the event rather than risk further damage.

The Australian has a history of back issues, withdrawing from the BMW Championship in 2014 with a similar complaint.

He almost withdrew from both The Barclays in 2015 and the World Golf Championships Dell Match Play in 2016 with the same issue before fighting through the pain and actually winning.

While the move was mostly precautionary he will enter East Lake under an injury cloud.

“He’s all right, he’s just got some back issues and is in a little bit of pain. He’s getting treatment right now. I don’t think it’s anything that he hasn’t dealt with before,” Day’s manager Bud Martin said.

“The trainer is maybe thinking it’s the same type of thing that he dealt with I think at the Barclays and last year where he picked something up in his bus and it kind of got out of line.

“But just better safe than sorry. Instead of forcing it, we just decided that it was more prudent to kind of come in, get it worked on, and deal with it.”

Martin would not speculate whether Day would be at full strength for the finale of the FedExCup Playoffs.

Day started the week at No. 2 on the FedExCup points list, hopeful of remaining inside the all-important top 5 headed to East Lake.

Those in the top 5 can guarantee the FedExCup with a win in the TOUR Championship.

With zero points he is now projected fourth but could potentially fall as low as sixth if Paul Casey wins the BMW Championship and Jordan Spieth makes a big back nine run up the leaderboard.

“We’ll probably get a MRI just to double check. My gut is that he’ll be fine,” Martin said.

“Hopefully, he’ll be ready for Atlanta, but the most important thing is the next 15 years, not the next 15 days.”