(Reuters) - An on-going back injury prompted world number one Jason Day to pull out of the Tour Championship during the second round in Atlanta on Friday.
Day withdrew while playing the eighth hole at East Lake.
The Australian picked up his ball in the rough, shook hands with fellow competitor Kim Si-woo and walked back to the clubhouse.
Day, 28, also withdrew during the final round of his previous tournament, the BMW Championship two weeks ago.
Before the start of the Tour Championship, Day said his back was an on-going problem due to a bulging disc that caused occasional flare-ups.