(CNN) -- Former World No.1 Vijay Singh says he has been left '"shocked" and "angry" after the revelation that he used a spray which may have contained a banned substance under the PGA TOUR Anti-Doping Policy.
The PGA Tour said Wednesday that it was investigating claims that Singh had used a banned drug contained in deer antler spray.
The 49-year-old Fijian star told Sports Illustrated that he used the spray "every couple of hours..every day."
He is quoted as saying: "I'm looking forward to some change in my body. "It's really hard to feel the difference if you're only doing it for a couple of months."
But the spray is reported to be contain a substance called IGF-1, which is a "natural, anabolic hormone that stimulates muscle growth."
IGF-1 is banned by several professional sports organizations, including the PGA Tour.
In a statement issued through the PGA Wednesday, Singh said he had no idea that the spray may contain a banned substance.
"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," said the statement.
"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. I will not be commenting further at this time."
Two years ago, 1999 British Open champion Mark Calcavecchia was advised by golf officials to stop using the spray.
It is manufactured by an Alabama-based company Sports With Alternatives to Steroids (SWATS), who have links to other major sports in the United States.
CNN Senior Managing Editor of Medical News Tim Langmaid says the spray, which is also known as deer velvet, is purportedly used to boost strength and endurance, while it also improves immune system function.
He said: "It contains small amounts of deer IGF-1, or Insulin-like Growth Factor-1, which mediates the level of HGH in the body.
"It comes from the deer velvet that covers the growing bone and cartilage that develop into deer antlers.
"It's the IGF-1 that is on WADA's banned substance list. Excessive use in humans can lead to metabolic dysfunction, including glucose intolerance."
The spray is derived from deer harvested in New Zealand.
The Sports Illustrated article claimed Singh paid $9,000 for the product.
A PGA spokesman told CNN that the "matter regarding Mr Singh is pending review" but could not give an indication of how long the investigation would take.
"There is no timetable at the moment," he added
The 49-year-old Singh was scheduled to play in the Phoenix Open in Arizona starting Thursday, but pulled out citing a back injury, the PGA Tour website reported.
Singh's illustrious career has in the past been dogged by controversies, not least back in 1985 when he was banned from the Asian Tour over allegations he changed his scorecard to his advantage during a round.
He shrugged off that setback to gradually make his mark, first on the European Tour, then over in the United States, where he has campaigned on the PGA Tour since 1993.
He has won three majors and was the money list winner in 2003, relegating Tiger Woods to second spot.
But the same year, Singh's veiled criticism of women's No.1 Annika Sorenstam for competing against the men in the Colonial tournament led to negative publicity.
However, in 2004 Singh took the No.1 spot in the rankings from Woods and won the PGA Championship, his final major.
Despite his advancing years, he qualifies for the Champions Tour next month, Singh has continued to compete at the highest level of golf and is regularly in the upper reaches of the leader board in PGA events.