SCOTTSDALE, Ariz. -- Vijay Singh has withdrawn from the Waste Management Phoenix Open, a day after saying he used deer-antler spray.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.''
Meanwhile, Former British Open winner Bob Charles of New Zealand says he used and promoted a banned deer-antler spray for more than 20 years and is surprised to learn it contains a substance that violates golf's doping protocols.
The 1963 Open winner was a spokesman for the deer-antler product and used it daily over two decades.
He said he was ''totally unaware of illegal substances ... being in the horn or the antler of the deer. I take one or two deer velvet capsules daily and have been doing so for virtually 20 years or more.''
Also Thursday, Mark O'Meara said he doesn't think Singh would ever try to cheat but still believes the Fijian should be suspended ''for a couple of months'' by the PGA Tour for admitting he used deer-antler spray.
O'Meara, who called Singh a friend, said he heard about the Fijian's admission on Wednesday while preparing for the Omega Dubai Desert Classic, but doesn't believe he benefited on the course from the unorthodox treatment.
''I was obviously a little bit surprised with what I heard, but I don't think Vijay is a guy that would ever take advantage of anything. I know Vijay,'' O'Meara.
''I guess they could probably suspend him for a couple of months. I would think so,'' the two-time major winner said. ''Listen, people have had to pay the price before and he should be no different. If that is the case and the commissioner and tour feels he should be suspended for X amount of time, I think Vijay is man enough that he'll do that.''
Singh, who won the last of his 56 titles in 2008, said he will cooperate with the tour's review of the issue.
Despite Singh's admission, O'Meara and other golfers said they felt the measures in place to combat doping in golf, including random testing, were adequate.
''I don't think doping is a problem in golf whatsoever. I really don't,'' Paul Casey said. ''There are so many facets to our sport. Why was he taking it? Was he taking it to recover from injury? It doesn't help you get the ball in the hole at the end of the day. This is the first case I've heard where a guy admitted to taking anything.''
The oddity of deer-antler spray being used by golfers was the talk on the Dubai course on Thursday, with Lee Westwood among the players having a good laugh about it. Most said they had never heard of it until the story on Singh.
''Deer-antler spray? That sounds like something you wax your car with, doesn't it?'' Westwood said. ''I've never heard of it. ... You have to be careful about what you take. I try not to take anything now, really, other than Corona and vodka.''
Colin Montgomerie, a rival of Singh during their heydays, called the whole case ''odd'' and said the European Tour doctor ''came to us (and said) deer antler, whatever it is, don't take that this afternoon lads.''
Montgomerie said the tour had nothing to worry about with him when it came to doping.
''I can only speak for myself and it's not widespread within the Montgomerie family,'' the 2010 Europe Ryder Cup captain said, looking down at his torso. ''Unfortunately. You can see that though, can't you, really.''