World number six Jason Day is still hopeful of being fit for the Tour Championship despite suffering a back injury.
The Australian withdrew from the BMW Championship on Friday, midway through his second round at the Cherry Hills Country Club.
Day, 26, will still qualify for the final FedEx Cup event " the Tour Championship " despite his withdrawal.
Despite what is believed to be a lower back strain, Day said he still wanted to compete in Atlanta starting Thursday.
"I am extremely disappointed to have to pull out of this event," he said in a statement.
"I will be getting treatment on my back over the next few days and hopefully be ready for the Tour Championship."