Jamaican sprinter Asafa Powell has pulled out of the World 100m event in South Korea because of a groin injury, according to his agent.
The 28-year-old suffered the injury in Budapest at the end of last month.
His agent, Paul Doyle, said: "Asafa is very disappointed to say the least. He was really hoping to be able to run in what was going to be one of the most anticipated races of the championships."
Doyle also said that Powell may however recover in time to run in the 4x100m relay.
Powell is the fastest 100m runner in the world this year - clocking 9.78 seconds at the Diamond League meeting in Lausanne in June.
He was therefore expected to challenge world record holder and compatriot Usain Bolt for the 100m crown after American Tyson Gay also pulled out of the event because of a hip injury.
When told of Powell's absence, Bolt said: "Asafa's out? That's the first I heard of it."
The World Championships begin in Daegu on Saturday.
