In-form Will Zalatoris withdrew during the US PGA Tour's BMW Championship on Saturday after suffering a back injury, organiser said.
Zalatoris, who ended his long wait for a tour victory by winning last week's St. Jude Championship in a playoff, was injured on the fourth hole of Saturday's third round.
The 26-year-old, the current leader in FedEx Cup playoff points, received treatment after playing his second shot.
The PGA Tour later confirmed Zalatoris had withdrawn from the tournament with a back injury.
Zalatoris had started the third round at Wilmington Country Club five shots adrift of leader Adam Scott.