Diamond League - London Grand Prix
Venue: Crystal Palace Dates: 13-14 August
Coverage: Watch Live on BBC 2 (Friday 1800-2100 BST), BBC 1 (Saturday 1300-1630 BST) and BBC Sport website (UK users only); full commentary on 5 live sports extra on Friday, updates on Radio 5 live on Saturday
Powell has been struggling with a series of injuries in recent weeks
Jamaican Asafa Powell has pulled out of the 100m at the Diamond League meeting in London on Friday because of injury.
The 27-year-old former world record holder has a back problem that also led to him withdrawing from last Friday's Diamond League meeting in Stockholm.
He said he has had a series of injuries linked to a groin problem and is monitoring his fitness "day by day".
With Usain Bolt also out of action, Tyson Gay is now a strong favourite for the 100m at the London Grand Prix.
Other world-class performers competing in the two-day meeting, which gets under way at Crystal Palace on Friday, include in-form American 110m hurdler David Oliver and 200m runner Allyson Felix.
The only two athletes still in with a chance of winning all seven legs of the Diamond League - American shot putter Christian Cantwell and Croat high jumper Blanka Vlasic - are both in action.
Britain's Mo Farah, the new European 5,000m and 10,000m champion, takes on Kenyan-born American Bernard Lagat in the 3,000m on Friday.
And Welsh duo David Greene and Rhys Williams, fresh from their one-two in the European Championships, will be looking to confirm their step up to world class when they face world leader Bershawn Jackson in the 400m hurdles.
Saturday's highlights include new European champion Andy Turner tackling Oliver in the 110m hurdles while Britons Michael Bingham and Martyn Rooney, who finished second and third in the European Championships, go in the 400m.
They will face former Olympic champion Jeremy Wariner and Jamaican Jermaine Gonzales, who heads the world rankings with a time of 44.40 seconds.
World and Olympic 100m champion Bolt had already decided not to compete at the event before his season was ended by a back injury earlier this week, while Powell pulled out on Thursday.
"I am disappointed that I will not be able to run at the London Grand Prix as I love running in front of the Jamaican fans here," said Powell.
"I visited the doctor on Wednesday and he has advised me not to run in order to help the recovery of my injury. I had hoped it would be better but unfortunately this is not so."
The absence of the two Jamaicans leaves American Gay as the undoubted sprint star at Crystal Palace and he heads into the meeting brimming with confidence after his first ever victory over world record holder Bolt in Stockholm last week.
Nobody's ever run sub-13 seconds here in the UK - there's a reason for that
110m hurdler David Oliver
On Thursday the American said the win "was very important for myself, and also for the sport".
The three-time world champion added: "I know this may sound weird but I have received more attention for that victory than I did when I won (gold in the 100m, 200m and 4x100m) in the 2007 World Championships.
"That race, even though there weren't any medals on the line, it really meant a lot to people and to the fans of the sport. I got to see other people happy. It was a good day for the sport."
Sprint hurdler Oliver is in superb form after clocking 12.89 seconds - just 0.02 seconds off Dayron Robles's world record - in Paris last month.
But the American cautioned against fans expecting a repeat performance given the unpredictable weather in the United Kingdom.
"Nobody's ever run sub-13 seconds here in the UK. There's a reason for that," Oliver said.
"There have been some great hurdlers that have run here so the conditions really dictate who is going to run what. I can't really worry about the times, just about getting the win."