CHASKA, Minn. -- Paul Casey of England, the world's No. 3 player, withdrew Thursday from the PGA Championship because of a rib injury.
Casey, a three-time winner this year on the PGA and European tours, first strained a 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 the Bridgestone Invitational in Akron, Ohio.
Casey said after withdrawing Thursday that he feels fine when he's 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 can't 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 don't push it too quickly."
He planned to return to Phoenix later Thursday and have tests done to make sure the injury is a pulled muscle and not something more serious, such as a cracked rib.
"I don't 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 by Tim Petrovic.
Alternates Jason Day and George McNeill had decided not to go to Hazeltine National. With Casey withdrawing and being replaced by Petrovic, Tim Herron, who grew up 15 minutes away in Wayzata, became the first alternate.
Herron, the only PGA Tour player who lives in Minnesota, did not qualify and was not given an invitation. His ranking is 222nd.