American sprinter Tyson Gay has withdrawn from the World Championships in Moscow, after he admitted on Sunday that he has tested positive for a banned substance.

The American 100 meter world-leader has refused to name the substance but the admission came after he was notified by the US Anti-Doping agency that his test from May 16th - a routine out of competition test - had returned as positive.

Gay's 'B' sample has yet to be tested, but it is believed that this will confirm his guilt, and he will then have to wait for any ban that will follow.

The 30-year-old was in fantastic form ahead of the Championships, winning the 100 meter and 200 meters in the national championships just last month. He also holds the three fastest 100m times this year.

He was in no mood to refute the claims, and was close to tears as he revealed all this weekend in a dramatic phone call. 

The Associated Press report Gay as saying: "I don't have a sabotage story. ... I basically put my trust in someone and was let down."

After carding a world best in 2013 of 9.75 seconds in the nationals, the American will be devastated to have to pull out of the World Championships, especially after winning the coveted sprinter's triple of the 100, 200, and 4x100 metre titles in Osaka six years ago.

The revelation comes as sources from Jamaica also confirm that four athletes, two throwers and two sprinters, have also had their 'A' samples come back as positive.

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