Jason Day has experienced better years physically. From the flu to various colds and other nagging ailment, it's been a rough one for the world's No. 1 player.

On Sunday, he withdrew from the BMW Championship with an apparent back injury. He was 2 over through eight holes on the day. He was 3 under for the tournament and 16 strokes back of leader Dustin Johnson.

This does not affect his standing for the Tour Championship in two weeks. He will participate and apparently not fall out of the top five for that event. The significance there is that anyone in the top five controls his own destiny for the FedEx Cup and the $10 million prize. If Day wins the Tour Championship, he will also win the FedEx Cup.

Still, you never like to see the world's top players (or anyone, for that matter) injured. Day will have two weeks off -- there is a break between the BMW Championship and Tour Championship -- before teeing it up with the final 30 players at East Lake.