The 27-year-old Ethiopian was expected to make her marathon debut, but says ''the increase in mileage has caused a flare-up of my previous lower leg injury.''
Dibaba is a three-time Olympic champion, having also won the 5,000 and 10,000 at the 2008 Beijing Games.
London Marathon race director Hugh Brasher says ''it is disappointing to lose Tirunesh ... everyone was full of anticipation to see how well she performed in a marathon.''
Olympic marathon champion Tiki Gelana will lead the Ethiopian challenge in the British capital. World champion Edna Kiplagat is competing along with world and Olympic silver medalist Priscah Jeptoo.
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