Mark Lewis-Francis has pulled out of today's Norwich Union London Grand Prix with a hamstring problem.

The 22-year-old is struggling to shake off the effects of the pull he sustained at the AAAs in Manchester nearly two weeks ago and with the World Championships in Helsinki at the start of next month, he has decided not to run at Crystal Palace as a precautionary measure.

The Birchfield Harrier is, however, confident that he will recover in time for those Championships, which begin on August 6.

Lewis-Francis has had a roller-coaster year so far having set a season's best of

10.10 seconds for the 100 metres, winning his first 200m race for three years and beating three-time world champion Maurice Greene twice.

But there have also been low points with his failure to overcome Jason Gardener at Sports City, a disappointing run in the Super Prix in Athens last month and this most recent fitness concern meaning he goes to Finland with a lot to prove.

The Olympic relay gold medallist had been due to face new world record holder Asafa Powell and Olympic champion Justin Gatlin although America's Olympic finalist Shawn Crawford has also pulled out of the meeting.

Powell will have has his own 100m world record in his sights when he lines up on Friday. Powell became the fastest man on the planet when he broke Tim Montgomery's three- year- old record in Athens' Olympic Stadium five weeks ago.

He clocked up 9.77 seconds on that occasion - one hundredth of a second faster than the American - but is bidding to go even quicker.

The 22-year-old, who has been nursing a groin injury, said: "I'm confident I can beat my world record but it's too early to say where I'm going to do it.

"But I feel good now, like the old Asafa Powell. Last year was my first time at Crystal Palace and I equalled my personal best so let's hope I can do the same thing again."