Former double sprint world champion Tyson Gay is pulling out of next month's championships in Moscow following a failed drug test.<br/> <br />The American athlete said Sunday that the issue centred on a May out-of-competition sample and that he could not identify the substance.<br/> <br />A second sample from the same period has yet to be tested.<br/> <br />Gay, who had this year's fastest 100 metre sprint time of 9.75 seconds, holds the joint title of second fastest man in the world.<br/> <br />U.S. track and field officials said they were disappointed about the news ahead of a major event.<br/> <br />Jamaican sprinter Asafa Powell has also tested positive for a banned stimulant.<br/> <br />His agent told Reuters Sunday that Powell's team is now investigating how the substance got into his system during last month's national championships.<br/> <br />Jamaican compatriot and Olympic medallist Sherone Simpson admitted she had tested positive during the event as well.
