Vijay Singh withdrew from the Phoenix Open before the start of the first round on Thursday, a day after he admitted using a deer antler spray that contains a substance banned by the PGA Tour.
Singh, a two-time winner of the tournament, cited a back injury as the reason for this withdrawal.
However, his departure means the 49-year-old from Fiji has yet to face reporters since he confirmed on Wednesday that he used the spray -- while insisting he didn't know it contained anything that contravened the tour's anti-doping regulations.
In a Sports Illustrated article published Tuesday, Singh was linked to a two-man company called Sports with Alternatives to Steroids (SWATS) and its deer antler spray that purportedly helps athletic performance.
The spray contains IGF-1, an anabolic hormone that boosts muscle growth and is banned by all major sports organizations.
Singh said Wednesday that he was cooperating with a PGA Tour investigation into the matter.
Singh is next scheduled to play at Pebble Beach next week. His 34 career PGA triumphs include three major titles, at the 2000 Masters and the 1998 and 2004 PGA Championships.