Vijay Singh says he is angry with himself for using deer antler spray
Former world number one Vijay Singh says he is angry with himself after admitting using a substance banned by golf's anti-drug abuse rules.
An online article by the American magazine Sports Illustrated detailed use of "Deer Antler Spray" by Singh.
The Fijian is now facing a suspension.
In a statement, 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."
According to Section One of the Tour's Anti-Doping Program Manual, a player is strictly liable whenever a prohibited substance is in his body, regardless of the circumstances.
Deer Antler Spray is manufactured by the controversial company Sports with Alternatives to Steroids (SWATS).
In promotional material the firm claims the substance contains IGF-1, a natural anabolic hormone that stimulates muscle growth.
IGF-1 is on golf's banned list.
The sport's drugs policy is in line with the code set out by the World Anti-Doping Agency.
In the SI article Singh, 49, was quoted saying he used the product "every couple of hours... every day."
His statement continued: "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.
"In fact, when I first received the product, I reviewed the list of ingredients and did not see any prohibited substances.
"I have been in contact with the PGA Tour and am co-operating fully with their review of this matter. I will not be commenting further at this time."
Former Open Champion Mark Calcavecchia ended his promotional link with the product after being warned by the Tour in 2011.
Singh may now be liable to a suspension from pro golf. Since drug testing was introduced in golf in 2008 only one player has been banned for violating the code.
American journeyman pro Doug Barron received a one-year suspension after failing a drugs test at the St Jude Classic in 2009.
Barron was taking Lyrica as a substitute for propranolol, a banned substance and exogenous testosterone, which he received by an injection from a doctor.
He had been prescribed propranolol since the age 17 but an earlier attempt to gain a medical exemption had been denied by the Tour.
Singh spent 32 weeks as world number one between 2004 and 2005, won the Masters in 2000 and the 1998 and 2004 PGA Championship.
He is due to compete in the Tour event in Phoenix which starts on Thursday.