England's Paul Casey withdrew from the US PGA Championship due to a rib injury today just hours before he was set to tee up in the opening round at Hazeltine.

The world No3 has been struggling since straining a muscle preparing for last month's Open Championship at Turnberry.

Despite playing nine practice holes yesterday he did not feel fit enough to make his tee-off time this afternoon and his place has gone to American Tim Petrovic.

Casey said: "I'm very disappointed but I have to look at the bigger picture which is the fact that I will play a lot more majors over my career and I have to be ready for what is coming up the rest of the season with the FedEx Cup and The Race to Dubai.

"But it is very frustrating because standing there hitting easy golf swings it is not that bad. It is just starting to pull when you are getting to six irons and longer.

"If it is doing that on a flat lie on the range, then I can't risk it on the golf course.

"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."

Casey said he had given himself every chance to compete.

"I feel good that I tried everything to try and get it ready and I also gave Tim Petrovic an hour.

"He was out there warming up alongside me so I went to speak to him myself and told him to go and play well."