The PGA Championship
Venue: Hazeltine National Golf Club, Minnesota Date: 13-16 August
Coverage: Live on BBC Radio 5 live; scorecard updates and reports on the BBC Sport website
Casey sustained the injury while preparing for the Open in July
England's world number three Paul Casey withdrew from the USPGA Championship an hour before the start on Thursday after failing to shake off a rib injury.
The 32-year-old was due to tee off at 1345 BST but the strain inhibited him when he warmed up with longer irons.
He suffered the original injury before the Open in July and was only able to play nine holes in practice.
"I'm very disappointed but I have to look at the bigger picture," said Casey, who is replaced by Tim Petrovic.
The advice I have been given from the experts and a lot of the players is don't push it too quickly
"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.
"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."
Casey was also forced to pull out of last week's World Golf Championships after six holes.
He joins 2008 Masters champion Trevor Immelman, who pulled out with a recurring wrist injury, among the absentees at Hazeltine.
The South African misses his third straight major and his place in the draw goes to Bob Estes.