England winger David Strettle is definitely out of the World Cup after breaking a bone in his left foot.
Strettle has impressed since breaking into the England side
The Harlequins player will have a screw inserted into his fractured fifth metatarsal and will be out of action for 12 weeks.
"I'm desperately sorry for Dave as I'm sure he would have made a huge contribution to our World Cup campaign," said coach Brian Ashton.
England must name their definitive 30-man World Cup squad on Tuesday.
At the moment, Ashton has no plans to call up a replacement for Strettle.
His absence means that it looks certain Paul Sackey, Josh Lewsey, Jason Robinson and Mark Cueto will fill four of the back-three slots with Nick Abendanon and Danny Cipriani possibly facing a straight fight for a fifth berth.
Despite what he described as "a massive disappointment", Strettle said he was determined to focus on the future.
"All I want to do now is hope that the operation goes well and then start to get myself fit to play for Harlequins again as soon as I can," he told the Rugby Football Union website.
Strettle, 24, who has three caps, has made a big impression since coming into the England team for the Six Nations game against Ireland, after Jason Robinson suffered a neck injury in training.
But he has also endured some bad luck, missing both England's Tests against South Africa after being hospitalised with a stomach virus which forced him home from the tour.
As soon as the nature of the injury became clear, his chances of playing in the World Cup were put in serious doubt.
England footballers David Beckham and Wayne Rooney both endured seven-week absences when they suffered similar injuries before the 2002 and 2006 World Cups respectively.
Even if he had returned that quickly, Strettle would have missed all England's group-stage games.
Gloucester centre Mike Tindall also looks set to miss the tournament, having struggled to regain fitness since breaking his leg in April.
Mark Cueto (groin), Tom Rees (hamstring) and Peter Richards (back) are also currently battling against injury, but are not thought to be such long-term worries.
Ashton has already ruled uncapped Bristol number eight Dan Ward-Smith out of his World Cup plans after he failed to recover in time from a knee injury.