Former world number one Vijay Singh has admitted using deer antler spray, but says he was unaware the extract contained an insulin-like growth factor that is banned by the PGA Tour.
Fijian Singh, a three-times major winner, has been using the spray, which is believed to speed up recovery from injury, for "a couple of months," according to a Sports Illustrated article published online earlier this week.
The spray is produced by Sports with Alternatives to Steroids (SWATS) and contains extract contains 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," Singh, who has battled assorted health problems in recent years, especially with his back, said in a statement on Wednesday.
"In fact, when I first received the product, I reviewed the list of ingredients and did not see any prohibited substances.
"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 launched its anti-doping programme in July 2008 and said, in the event of a positive doping test, it would disclose details only after the entire appeals and challenges process was completed.
The variety of sanctions could include disqualification, a one-year suspension for a first violation, up to five years for a second violation and a lifetime ban for multiple violations, plus fines up to $500,000.
In August 2011, the Tour warned players about using deer antler spray with its prohibited ingredient after veteran players Mark Calcavecchia and Ken Green had both endorsed SWATS' so-called "Ultimate Spray."
The Tour could not be immediately reached for comment. Deer antler extract became a hot topic earlier this week when National Football League linebacker Ray Lewis was among a handful of athletes accused by Sports Illustrated of using the spray.
Lewis swiftly dismissed the report which quoted Mitch Ross, co-owner of SWATS, as saying the linebacker asked for products to speed his recovery from a torn triceps in October, including deer-antler extract.
In that same article, Singh was described as one of the few athletes who had compensated SWATS for their products, allegedly paying Ross $9,000 in November for the spray, chips, beam ray and powder additive.
"I'm looking forward to some change in my body," Singh was quoted as saying by Sports Illustrated.
"It's really hard to feel the difference if you're only doing it for a couple of months."
Since the PGA Tour's anti-doping programme was launched, 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.
Singh, a 49-year-old who is renowned for his workaholic approach to the game, is scheduled to play in the PGA Tour's Phoenix Open this week in Scottsdale, Arizona.