He notified tournament officials of his decision minutes before his 9:05 a.m. ET tee time at Valhalla Golf Club. He was replaced by first-alternate John Huh, who had spent the early part of the week waiting to see if Tiger Woods, also hampered by a bad back, would compete.
Kuchar tied for 12th place last week at the WGC-Bridgestone Invitational and was one of the favorites to contend here this week as he looked for his first major championship victory. He has six career top-10 finishes in major championships, all coming since 2010.
At fifth in U.S. Ryder Cup standings, Kuchar is a lock to make the team. The top nine at the end of the PGA Championship automatically qualify for the team.
Kuchar's best PGA finish is a tie for 10th in 2010 at Whistling Straits. It's one of his six career top-10 finishes in majors.