Vijay Singh has been forced to withdraw from the Waste Management Phoenix Open and faces a worldwide ban after admitting using a banned spray.
The 49-year-old revealed he had used a deer antler spray which has previously been found to contain a banned growth hormone.
The Fijian pulled out before the start at TPC Scottsdale and issued a statement claiming he had no idea the spray contained an illegal 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," he said.
"In fact, when I first received the product I reviewed the list of ingredients and did not see any prohibited substance.
"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 co-operating fully with their review of this matter. I will not be commenting further at this time."
Deer antler spray has been found to contain the banned IGF-1, a natural anabolic hormone that stimulates muscle growth.
Following Singh's withdrawal, former Open champion Bob Charles admitted he had used and promoted the antler spray for more than 20 years without knowing it contained a banned substance.