Louisville - American Ben Crane, a PGA Tour winner in June at Memphis, withdrew on Friday from the PGA Championship due to back issues, becoming the fourth US player to quit the event.
Crane, who fired an opening-round 74, won his first title since 2011 at the St. Jude Classic nine weeks ago.
The field of 156 saw former winner David Toms withdraw on Tuesday while sixth-ranked Matt Kuchar pulled out with back issues before Thursday's final round.
After playing only 10 holes, the last of them a triple-bogey at the 10th, defending champion Jason Dufner pulled out of the tournament on Thursday due to a neck injury that has nagged him since the Masters.
And 14-time major winner Tiger Woods, who withdrew from the final round of last week's World Golf Championships event, had been questionable until arriving on the eve of the event and declaring himself fit after a nine-hole practice round.