Eugene Oregon: Tyson Gay's hopes of an Olympic sprint double ended in agony on Saturday.

The 200 metres world champion crashed out of the US trials when his leg seized up during the quarterfinals.

Gay tumbled to the track about 40 metres into the race.

His agent later said the problem was severe cramp in his left hamstring.

The injury means Gay will now compete in just the 100 metres and 4x100 relay at next month's Beijing Games.

Gay said: "Before I went out on the track I felt a little tightness in my hamstring so I kind of had a bad feeling.

"I felt it, sort of a pull, about 40 metres," added the 25-year-old.

Heading to his hotel immediately to receive treatment, Gay was lucky enough to suffer no further damage, agent Mark Wetmore said.

The setback is a major blow to US hopes in Beijing.

Gay's injury has once again brought the the strict American qualifying procedure into the spotlight and re-opened the debate over whether the rules should be changed.

The US rules dictate that only the top three finishers at the trials make the Olympic team regardless of circumstances.

Athens Olympics

A similar situation deprived the United States of its top 200 metres runners at the 2000 Olympics, when world record holder Michael Johnson and then-100 metres holder Maurice Greene crashed out of the trials final with injuries.

Both missed the Sydney Games in the longer sprint but won gold in their first-choice events.

Gay had hoped to duplicate his 2007 world 100 and 200 metres titles at Beijing.

He showed he was ready to challenge Jamaican world record holder Usain Bolt and his predecessor Asafa Powell in the 100 metres by winning the trials in the fastest time under any conditions with a wind-assisted 9.68 seconds.

Gay is scheduled to meet Jamaican Powell over 100 metres in London on July 25.

In Gay's absence, Rodney Martin, Wallace Spearmon Jr and Walter Dix joined 2004 Olympic gold medallist Shawn Crawford in advancing to yesterday's final.

Martin clocked a wind-assisted 20.04 seconds in one semifinal with Spearmon finishing in 20.05 and Dix running 20.09.

Crawford won the other semifinal in 20.21 seconds.

Unlike Gay, world champion Allyson Felix eased into the final of the women's 200 metres after she recorded a brisk 22.22 seconds to lead all qualifiers from the semi-finals.

However, the 1996 Olympic 110 metres hurdles gold medallist Allen Johnson crashed out of his event.

He suffered a season-ending tendon injury after clearing four barriers in the opening round.

"Hopefully I'll be back next year," said the 37-year-old Johnson.

The four-times world champion added that these were his final Olympic trials.

Allen has represented the United States at three previous Games.

US indoor champion David Oliver posted the top quarter-finals time of 13.07 seconds, with two-time Olympic silver medallist Terrence Trammell among those advancing.