Tyson Gay tests positive for banned substance

Former 100m world champion Tyson Gay has tested positive for a banned substance.

The 30-year-old American has now pulled out of next month's World Championships in Moscow.

The sprinter was notified by the US Anti-Doping Agency on Friday that a sample taken in May has failed a test.

"I don't have a sabotage story," USNews.com quotes Gay as saying. "I basically put my trust in someone and was let down."

A second sample from Gay is due to be tested in the coming weeks.