Vijay Singh withdrew from the Phoenix Open on Thursday, a day after saying he used deer-antler spray and was "absolutely shocked" that it may contain a banned substance.
Singh cited a back injury in pulling out 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 the owners of Sports With Alternatives To Steroids $9,000 last November for the spray, hologram chips and other products.
The magazine also reported Baltimore Ravens linebacker Ray Lewis sought help from SWATS in his recovery from a torn right triceps. The company says its deer-antler substance contains a banned performance-enhancer connected to human growth hormone.
Singh said in a statement Wednesday that while he used deer-antler spray he was not aware he may have been violating the PGA Tour's anti-doping policy.
"In fact, when I first received the product, I reviewed the list of ingredients and did not see any prohibited substances," he said. "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. I will not be commenting further at this time."
PGA Tour spokesman Ty Votaw said the tour is "looking into the matter."
Singh won the last of his 34 PGA Tour titles in 2008. The three-time major champion also has 22 international victories. Early in his career, he was suspended from the Asian Tour for two years for altering his scorecard during a tournament in Indonesia.
Doug Barron is the only player to be suspended under the tour's anti-doping policy, missing part of 2009 and most of 2010. The one-year suspension was lifted in September 2010, and Barron was granted a therapeutic use exemption for low testosterone.