Vijay Singh withdraws from Phoenix Open

Fiji's Vijay Singh has withdrawn from the Phoenix Open with a back complaint.

Singh had reportedly been under investigation by PGA officials after he admitted to using a product that contained a banned substance.

The 49-year-old has revealed that he has been using "Deer Antler Spray", which contains a hormone that stimulates muscle growth.

If found guilty, the three-time Major winner could face a lengthy suspension from worldwide competition.