Jason Day's confident his back is at full strength for the Tour Championship.

The world number one heads into tomorrow's event in Atlanta, fourth on the FedEx Cup standings, but a win at East Lake would be good enough for him to snatch the $10 million bonus.

Despite pulling out of the final round of the BMW Championship with a sore back, Day says he's fully fit and it won't effect his play.

He says he's never hurt his back actually swinging a club, but rather from small mundane tasks in life.

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American Dustin Johnson leads the FedEx Cup standings with compatriot Patrick Reed second and Australian Adam Scott third.