Olympic sprinter Yohan Blake of Jamaica has withdrawn from the world championships in Moscow next month due to a nagging hamstring injury.

Agent Cubie Seegobin says that although Blake has made "vast improvement" since injuring the leg in April, he needs more time to fully recover.

Blake also pulled out of the island's national championships last month because of his hamstring. He qualified for the August meet by winning the 100 metres at the 2011 world championships.

Blake ran the 100 in 9.69 seconds last season, tying U.S. sprinter Tyson Gay as the second-fastest man in history behind Usain Bolt.

Blake's withdrawal Tuesday follows news over the weekend of positive tests for Gay and top Jamaican sprinters Asafa Powell and Sherone Simpson.