(Reuters) - Vijay Singh pulled out of the Phoenix Open on Thursday before the start of the first round, a day after admitting he had used deer antler spray which contains an ingredient banned by the PGA Tour.

The former world number one, who was scheduled to tee off in the company of American Ryan Moore and Swede Carl Pettersson at the TPC Scottsdale, cited a back injury for his withdrawal.

Vijay Singh of Fiji smiles as he looks at the Fedex Cup after the conclusion of the Tour Championship golf tournament at East Lake Golf Club in Atlanta, Georgia, September 28, 2008. REUTERS/Tami Chappell

Singh, 49, was replaced in the field by American Richard H. Lee.

A three-times major winner, Fijian Singh revealed earlier this week he had been using deer antler spray for a couple of months in an interview with Sports Illustrated magazine.

On Wednesday, he issued a statement in which he expressed shock that the spray contained 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," said Singh, who has battled assorted health problems in recent years, especially with his back.

"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 is now "looking into the matter" and has a variety of sanctions at its disposal, including disqualification, a one-year suspension for a first violation and up to five years for a second violation.

Since the Tour's anti-doping programme was launched in 2008, 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.

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Frank Pingue)

• Please wait.

• Grace hammers home a point with two golds
• McGinley raises Ryder Cup picks from two to three
• Governing bodies to prohibit anchoring of putters from 2016
• China crush arch rivals Indonesia
• China to host seventh edition of Royal Trophy
• Former Asian phenom takes slow route to success
• South Korean captures first US PGA title with a 69
• Spurs thump Grizzlies in series opener
• Uihlein rules at Madeira Open
• Malaysia have their work cut out in the World League