Gay, 28, withdrew before his semi-final and is unlikely to run in the 200m - a distance he has conspicuously avoided running so far this season - meaning he would not be eligible for the sprints in Daegu, South Korea.

He could still run in the 4x100 metre relay at the event, which begins on August 27.

The former Olympic 100 metre champion Justin Gatlin is set to return for the US after a four-year drug ban, having finished second in a final won by Walter Dix in 9.94sec, with Michael Rodgers claiming the third and final place.

Gay, who has run the fastest 100m in the world this year of 9.79, had been expected to be one of the main challengers to the Jamaican world record-holder in South Korea.

Bolt, who has a wild card entry to the 100 and 200 metre events as defending champion, has not entered this weekend's Jamaican trials, where Asafa Powell shrugged off recent injury problems to win the 100 metres in 10.08 and will be joined in Daegu by second-placed Yohan Blakd, who ran 10.09, and Steve Mullings, who did 10.10.

Gay, whose US record of 9.69 makes him the second fastest 100 metre runner of all time behind Bolt, had qualified from his heat in a wind-assisted 10.01, second behind Ivory Williams and third fastest overall, but withdrew before the semi-final citing a recurrence of a problem in his right hip and adductor.

"I've been bandaging it up, couldn't really take anymore," Gay said.

"I decided to stay healthy.

"It's pretty painful running in pain."

Gay could still be part of the 4x100m relay team if he recovered in time, USA Track and Field (USATF) officials said.

"But he has to be able to show fitness and be able to run," said USATF President Stephanie Hightower.

"It is a big blow," said Dix of Gay's potential loss to the relay squad.

"Tyson at his best is one of the top runners in the world.

"We're going to have to step up."

Gay has been plagued by injuries since winning the 100m and 200m world titles in Osaka in 2007.

In 2008, he was injured during the 200m at the US Olympic trials and later that year failed to make the 100m final at the Beijing Games.

The following year, he pulled out of the 200m after taking 100m silver behind Bolt when he set his world record at the World Championships in Berlin.

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