Treble world champions Tyson Gay and Allyson Felix lead a host of stars in Saturday's 'USA versus the World' Penn Relays showdown, but world 100 metres record-holder Asafa Powell has pulled out of the event.

Nearly 150 athletes from 11 nations will compete in the annual elite session of the meeting, which the Americans have dominated in the past three editions, winning five of the six races each time.

The meeting features 4x100, 4x400, women's sprint and men's distance relays and will serve as an early test ahead of August's Olympic Games in Beijing.

Powell (pictured, right, with Gay) set the 100m world record of 9.74 seconds last September in Italy and will be joined by several fellow Jamaicans.

"We expect a full recovery shortly, but he has a very limited range of motion (now)," Powell's manager Paul Doyle said.

Powell, who suffered the injury lifting weights in Jamaica last week, was due to compete in a 4x100 relay at the meeting.

His next scheduled competition is a 100 metres at Doha on May 9th.

"He should be ready," Doyle said, "but it is one of those things -- you do not want to push him back too early because you could be right back to square one."

Powell also is scheduled to run the 100 in Oslo on June 6 and in Eugene, Oregon, two days later. Although the turnaround between the two races is short, "it is doable," Doyle said.

Michael Frater, the 2005 world 100m runner-up, will join countryman Powell as will 2004 Olympic 4x100m gold medalist Sherone Simpson, 2000 Olympic 4x400m bronze medalists Sanjay Ayre and Michael Blackwood and world relay veterans Novlene Williams and Shericka Williams.

The formidable American men are paced by Gay, a triple champion at last year's world meet, reigning Olympic and two-time world 400m champion Jeremy Wariner and 2007 world 400m hurdles champion Kerron Clement.

The US line-up also includes two-time world 200m medalist Wallace Spearmon, 2007 world 400m runner-up LaShawn Merritt and Darold Williamson, a member of the 2004 Olympic 4x400m relay winners.

Felix will be joined on the US women's side by 2006 IAAF Athlete of the Year Sanya Richards, 2005 world 100m champion Lauryn Williams, 2003 world 100m champion Torri Edwards, two-times world 100m hurdles champion Michelle Perry and 2005 world 400m runner-up Lashinda Demus.

Reuters / AFP