Citing a back injury, Vijay Singh withdrew from the Phoenix Open on Thursday, a day after saying he used deer-antler spray, but was unaware that it contained a banned substance. 

“In fact, when I first received the product, I reviewed the list of ingredients and did not see any prohibited substances,” Singh said Wednesday. “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.”

Deer antler spray contains the banned substance IGF-1.

PGA Tour spokesman Ty Votaw said the tour is “looking into the matter.” 

Singh, 49, has not won on the PGA Tour since 2008.

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