Reigning 100m champion Yohan Blake has withdrawn from August's World Athletics Championships in Moscow with a hamstring injury. The 23-year-old Jamaican pulled out of his country's national championships last month having been troubled by the injury since April. Blake won the 2011 title in Daegu when compatriot Usain Bolt false-started. Team-mate Asafa Powell and American Tyson Gay have withdrawn from the event in Moscow after positive dope tests. Gay's A sample from an out-of-competition test in May was positive, while Powell tested positive for a banned stimulant at June's Jamaican Championships. Both athletes are awaiting the results of their B samples. As defending champion, Blake did not have to qualify for the 100 metres at this year's World Championships, but he would not have competed in the 200 metres after pulling out of the Jamaican trials. Blake has not run in a competitive 100m this year, but he recorded 20.72 in the 200m in Kingston, Jamaica, on 8 June.