Italy's Francesco Molinari, the 2018 British Open champion, withdrew from the 103rd PGA Championship on Thursday with a back injury, tournament organizers announced.
The 38-year-old from Turin missed the cut in three of his past four starts and finished 52nd at last month's Masters.
American Brandon Hagy replaced Molinari in the field of 156 in the year's second major tournament, which began Thursday at Kiawah Island's Ocean course.
Hagy was set for an 8 a.m. (1200 GMT) start off the 10th tee alongside two-time major winner Zach Johnson and Scottie Scheffler in an all-American trio.
World number 144 Molinari, whose most recent victory came at Bay Hill in 2019, had his best PGA finish in 2017 when he was a runner-up to American Justin Thomas.
Hagy, ranked 177th, seeks his first US PGA Tour victory in his tournament debut. The 30-year-old's best career finish was second at the Honda Classic in March, when he finished five strokes behind Australia's Matt Jones.