Paula Radcliffe has been forced to pull out of her comeback race this month owing to illness.
The 37-year-old, who has not raced for 18 months, has been ruled out of the 10k Great Manchester Run on Sunday week because she has been suffering from a chest and throat infection.
The marathon world record holder had been set to compete for the first time since taking an extended break to give birth to her second child, Raphael, last September.
"I'm really, really disappointed to have to pull out," said Radcliffe, who is building up for an assault on the Olympic marathon gold medal in London next year, the major title missing from her collection.
"I have missed racing so much and was so looking forward to running in Manchester. However, frustrated as I am, I know that the main focus for me is next year's Olympic marathon and achieving a qualifying standard later this year."
Radcliffe, who last raced at the New York Marathon in November 2009 when she finished fourth, admitted she could not take any chances with the illness. "As an asthmatic I know that bronchitis, especially at altitude, needs to be treated with caution immediately," said the triple London marathon winner.
Radcliffe is now set to return in the London 10,000 on 30 May, when she will race on roads that make up the Olympic course.