Vijay Singh pulled out of the Phoenix Open on Thursday before the start of the first round, a day after admitting he had used deer antler spray which contains an ingredient banned by the PGA Tour.
The former world number one, who was scheduled to tee off in the company of American Ryan Moore and Swede Carl Pettersson at the TPC Scottsdale, cited a back injury for his withdrawal.
Singh, 49, was replaced in the field by American Richard H. Lee.
A three-times major winner, Fijian Singh revealed earlier this week he had been using deer antler spray for a couple of months in an interview with Sports Illustrated magazine.
On Wednesday, he issued a statement in which he expressed shock that the spray contained IGF-1 (insulin-like growth factor), a natural anabolic hormone that stimulates muscle growth.
"While I have used deer antler spray, at no time was I aware that it may contain a substance that is banned under the PGA Tour anti-doping policy," said Singh, who has battled assorted health problems in recent years, especially with his back.
"I am absolutely shocked that deer antler spray may contain a banned substance and am angry that I have put myself in this position. I have been in contact with the PGA Tour and am cooperating fully with their review of this matter."
The PGA Tour is now "looking into the matter" and has a variety of sanctions at its disposal, including disqualification, a one-year suspension for a first violation and up to five years for a second violation.
Since the Tour's anti-doping programme was launched in 2008, American journeyman Doug Barron is the only player who has been suspended for a violation. Barron, then 40, was banned for one year in November 2009 for taking a performance-enhancing drug.
(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Frank Pingue)