Day withdraws from Tour Championship with back injury

Jason Day's season is over.

The top-ranked golfer in the world was forced to withdraw from the Tour Championship on Friday after suffering a back injury.

Day shot an opening-round 67 and was in a tie for fifth when he "slashed a driver out of the rough, a move that appeared to trigger the injury," writes Golf Digest's Joe Beall.

The season ends with Day having won three tournaments and carding 10 top-10 finishes.

Dustin Johnson will win the points-based PGA Player of the Year award based on Day's withdrawal, according to the Associated Press.