Tyson Gay has pulled out of his showdown with Asafa Powell at Crystal Palace tomorrow night to raise doubts about whether the 100 metres world champion will be fit to race for the Olympic title.

The American withdrew from the Aviva London Grand Prix and, while that is a massive blow for the organisers, the fear is that he will be undercooked for next month’s Games in Beijing.

Gay, who won the 100 metres and 200 metres as well as a 4 x 100 metres gold at the World Championships in Osaka, Japan last year, is struggling with the hamstring problem he suffered at the United States Olympic trials in Eugene, Oregon, this month.

Having qualified for the 100 metres via the sudden-death trials system, he fell to the track in the 200 metres clutching his left thigh. A scan showed that he had a mild strain of the semi-tendinosus muscle, but his mother, Daisy Gay Lowe, said at the time: “It’s going to work out. He’s going to run the 100 and he’s going to win the 100.”

Gay, 25, flew to Munich to be treated by Dr Hans-Wilhelm Müller-Wohlfahrt, the surgeon, who has helped Paula Radcliffe, the British marathon world record-holder. Gay had another scan on Monday that showed that the injury was healing well, but he was advised by his medical and management teams that a run in London tomorrow could wreck his Olympic hopes.

“I was really looking forward to getting back on the track again, and training has been going well,” Gay said. “I held out hope to run London, but progress has been steady and, with the first round of the Olympic 100 metres just three weeks away, I don’t want to risk doing anything to set things back. I apologise to the London fans.”

Mark Wetmore, Gay’s agent, played down fears that his man would be unfit for the Olympics. “The decision does not affect his plans for Beijing, by which time he is expected to be fully recovered,” he said.

Gay’s duel with Powell, of Jamaica, was one of the big draws at the London Grand Prix. Powell was looking forward to the race with added confidence after his victory over Usain Bolt, his compatriot and the 100 metres world record-holder, in Stockholm on Tuesday.

There will be still a top-class field this weekend, including Bolt, this year’s phenomenon, who runs the 200 metres on Saturday. However, Gay’s withdrawal will add to the criticism of the US trials system, which is breathless entertainment but sometimes forces athletes to put their wellbeing on the line.

Ian Stewart, London’s meeting director, took Gay’s decision on the chin. “Tyson gave himself absolutely every chance to be fit and I know he was absolutely desperate to run here,” he said.

Time will tell whether the move is a precaution or whether Gay is truly in trouble as he eyes a first Olympic medal.