Vijay Singh has withdrawn from the Phoenix Open, a day after saying he used deer-antler spray.
Singh cited a back injury in pulling out Thursday before the first round.
The 49-year-old Fijian first revealed he used the spray in an interview with Sports Illustrated. The magazine said Singh paid one of Sports With Alternatives To Steroids' owners $9,000 last November for the spray, hologram chips and other products. The deer-antler substance contains a banned performance-enhancer connected to human growth hormone.
Singh released a statement Wednesday at the Phoenix Open, saying: "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."
PGA Tour spokesman Ty Votaw says the tour is "looking into the matter."