Casey, a three-time winner this year on the PGA and European tours, first injured strained the rib muscle a week before the British Open. He has tried to let it heal with rest and treatment, but had to withdraw early in the first round a week ago at Firestone.
Casey said after withdrawing Thursday that he feels fine when hes taking easy swings. But he can still feel it pull on longer iron shots.
If it is doing that on a flat lie on the range, then I cant risk it on the golf course, he said. It seems like there has been a lot of guys who have had similar issues in the past, and the advice I have been given from the experts and a lot of the players is dont push it too quickly.
He planned to return to Phoenix later Thursday and have tests done to make sure the injury really is a pulled muscle and not something more serious, like a cracked rib.
I dont think it is that, he said, but we have to get it checked just to make sure.
Casey, who withdrew about an hour before his tee time, was replaced in the field by Tim Petrovic. He is the third player to withdraw at Hazeltine, leaving 97 of the top 100 players in the world at the final major. Robert Karlsson and Trevor Immelman previously withdrew.