Day bent over to put his tee in the ground and felt pain in his back. He withdrew as a precaution and was later diagnosed with a pinched joint capsule in his lower back.
According to Golf Channel's Todd Lewis, Day spent last week resting and getting treatment, and he is "cautiously optimistic" about playing this week at the Tour Championship.
Day also has a great shot to win his first FedEx Cup title. He's currently ranked fourth on the points list and can finish as low as third place and still have a chance of winning $10 million.