The much-hyped pre-Olympic 100m showdown between Tyson Gay and Asafa Powell at Crystal Palace this Friday is off after Gay pulled out.

The world champion picked up a mild hamstring strain at the US Olympic trials and has decided not to risk further injury before the Beijing games.

The race was expected to be the highlight of the two-day competition and act as a rehearsal for the sprint final next month.

However, with Gay injured and world record holder Usiah Bolt opting to run the 200m this weekend, Powell will be expected to record an easy victory.

British sprinters Marlon Devonish and Craig Pickering will be on the bill though alongside Sutton’s Harry Aikines-Aryeetey.