Olympic 10,000m champion Tirunesh Dibaba has been forced to postpone her marathon debut because of injury.
The 27-year-old Ethopian, who defended her Olympic title at London 2012, was due to run in her first competitive marathon in London on 21 April.
However, a recurrence of a lower leg problem has ruled her out of the race.
"The increase in mileage has caused a flare up of my previous injury but I look forward to making my marathon debut in London next year," she said.
Dibaba added bronze in the 5,000m at the London Games and captured the Great North Run half marathon last September.
She was aiming to become the first Ethiopian since her cousin Derartu Tulu in 2001 to win the women's race at the London Marathon but her withdrawal leaves Olympic champion Tiki Gelana to lead the Ethiopian challenge at her first appearance in the event.
Gelana will face World Champion Edna Kiplagat of Kenya, plus World and Olympic silver medallist Priscah Jeptoo in a race featuring five women who have completed the distance in less than two hours 20 minutes.
London Marathon race director Hugh Brasher said: "Of course, it is disappointing to lose Tirunesh.
"She has been such a fantastic athlete on the track, and everyone was full of anticipation to see how well she performed in a marathon, so we would be naturally delighted to see her return to London in 2014.
"We still have a fantastic women's race in prospect, however, with the Olympic and World Champions going head-to-head, and so many winners from major city marathons around the world."