Degitu Azimeraw, who won the Amsterdam Marathon in a course record as a 20-year-old last year, will miss the London Marathon after a positive Covid-19 test.
Azimeraw, who ran a stunning two hours, 19.26 minutes on her debut over the distance last October, had been hoping to challenge world record holder Brigid Kosgei and fellow Kenyan Ruth Chepngetich in the women's elite-only race being held on a multi-lap, bio-secure circuit in London's St James's Park.
However, she and Adelo tested positive in Ethiopia and were unable to join the chartered flight to London. Adelo has not been in contact with his athletes Shura Kitata and Alemu Megertu in the last two weeks so they are clear to stay in the secure, secret hotel and run on Sunday, race director Hugh Brasher told a teleconference.
Amid many measures being taken to minimise any infection risk, everyone involved in the race is using "bump technology" this week, where a device worn on a pendant records time spent in proximity to others. It allows organisers to warn athletes and operational staff if they are breaching social distance guidelines.
Sunday's race, the only major Autumn marathon to go ahead after widespread coronavirus cancellations, will see separate men's, women's and wheelchair races.
The big draw on Sunday is the head-to-head between world record holder and four-times London winner Eliud Kipchoge of Kenya and Kenenisa Bekele of Ethiopia, the only two men to have gone under two hours, two minutes for the distance.
Brasher said that many elements of Kipchoge's sub-two hour run in Vienna, also on a multi-lap course, last October had been incorporated into Sunday's race, where the athletes will run almost 20 laps, and where, weather-dependent, a fast time is expected.
Brasher said it was probably his proudest achievement in helping stage Sunday's race, which will be held alongside a "virtual event" where 40,000 people will cover the marathon distance at a venue of their choice.
They will be rewarded with finisher's medals as well as raising millions of pounds for charities hard-hit by the cancellation of the original marathon in April.
The mini-marathon, traditionally a low-key children's race held ahead of the main event and previously won by Mo Farah, has ballooned this year into 150,000 primary school children running 2.6 miles.