Paula Radcliffe has pulled out of her scheduled racing comeback at the Great Manchester Run on 15 May because of a recent illness.
The world marathon record holder, 37, has not competed for 17 months, during which time she has been recovering from injury and the birth of a second child.
She has been suffering from a chest and throat infection in the last week.
"I'm really, really disappointed. I have missed racing so much and was so looking forward to running," she said.
"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."
Recently crowned European indoor 3,000m champion Helen Clitheroe and European junior cross-country champion Charlotte Purdue will now lead the domestic challenge in the 10k race, against strong international opposition.
Radcliffe, who has been training at altitude in Albuquerque, New Mexico, added: "As an asthmatic, I know that bronchitis, especially at altitude, needs to be treated with caution immediately.
"Therefore, it is vital to get fully healthy and have a strong comeback race as soon as possible."
The Manchester event would have been Radcliffe's first competition since the New York Marathon in November 2009, when she finished fourth.
She has not yet made an announcement on her planned participation in the Bupa London 10,000 road race on 30 May.
She is expected to take part in a marathon later in the year as part of her plan to hit the qualifying standard for London 2012.
Radcliffe has held the world marathon record of two hours, 15 minutes, 25 seconds since 2003. She is also the world road-running 10km record holder, with a time of 30 minutes, 21 seconds.
There are expected to be 40,000 competitors for the Great Day of Sport on 15 May, which begins with the Great Manchester Run and includes the Great Salford Swim
The Great City Games later in the afternoon will feature elite athletes in a series of street sprints, including world and European heptathlon champion Jessica Ennis in the 150m and the hurdles.
British Olympic silver medallist and world 10k open water champion Keri-Anne Payne will compete in the mile-long swimming race in Salford Quays.