The 38-year-old Ethiopian, for whom London was due to be his first marathon since he ran 2 hours 01min and 41sec at the 2019 Berlin Marathon - just two seconds slower than the official world record set by his Kenyan rival in the previous year’s edition - said he was "disappointed" at having to withdraw.

"It has been a tough preparation time, with lockdown, when I couldn’t have my NN team around me," Bekele said.

"I was in good shape but then I picked up a niggle in my left calf after two fast training sessions close together in the last weeks of preparation.

"I have been having treatment every day since then and I truly believed I would be ready, but today it is worse and I now know I cannot race on it.

"This race was so important to me.

"My time in Berlin last year gave me great confidence and motivation and I was looking forward to show that again, I have worked so hard for it.

"I realise many people around the world have been looking forward to this race and I am sorry to disappoint my fans, the organisers and my fellow competitors. 

"I will take time to recover and become fit again and I hope to be back in London next year."

Virgin Money London Marathon event director Hugh Brasher said: "The world has been waiting to see this head to head between Kenenisa Bekele and Eliud Kipchoge but it will now not happen this Sunday. 

"We know how disappointed he is and we wish him a speedy recovery.

"This was never likely to be just a two-man race as we had four of the top ten fastest marathon runners ever and six men in the field who have broken 2:05, including Mosinet Geremew and Mule Wasihun, second and third last year, and 2018 runner-up Shura Kitata."

Home runner Chris Thompson is hoping several Britons can better the Olympic men’s qualifying time of 2:11:30 on Sunday and set up a "shoot-out" race next year ahead of the planned Games in Tokyo.

The 39-year-old, who took European 5,000 metres silver behind Mo Farah in 2010 and clocked 2:11:19 at the 2014 running of the London Marathon, represents one of the strongest home contenders on the closed, looped 1.3 mile course in St James’s Park.

The fastest British male, however, will be Jonny Mellor, who already has the qualifying time thanks to his 2:10:03 timing at Seville on February 24 this year.

Reflecting on the qualifying target during today’s virtual London Marathon press conference - a target established on July 28 when World Athletics ruled Olympic qualification for the marathon and road race walk events could re-start from September 1, three months earlier than previously announced - Thompson said: "Along with all the Brits here in the male and female races, I think everyone is looking for that allure of the Olympic standard.

"The fact that that opportunity has arisen has brought a lot of people here.

"Obviously World Athletics has extended the qualifying period, which has been a massive plus.

"So for me, without it being like a noose around the neck I kind of view it as a free hit, and let’s see what I can do.

"If I can be in Jonny’s shoes after the weekend I will be ecstatic, because imagine the scenario where there are a handful of British athletes with it and we are looking at a shoot-out in a marathon next year.

"I think it would draw quite a crowd.”

For home runners in the women’s elite race - who will be paying close attention to their alarms on Sunday morning given their 07.15am start time - the Olympic marker time is 2:29.30.

For Lily Partridge, who ran 2:29:24 in finishing eighth at the 2018 London Marathon, that is front and centre.

Steph Twell has already achieved that target, thanks to her time of 2:26:40 in Frankfurt last November in what was only her second marathon.

Twell - 15^th in last year’s 10,000 metres final at the Doha World Championships - has yet to confirm that the marathon will be her chosen path towards the postponed Tokyo 2020 Games.

"I haven’t left the track yet,” she said.

"I still think I’ve got unfinished business over the shorter distances.

"But I am still developing in the marathon, and I still don’t know my full potential in this event.

"My main aim for next year is to have the best impact I can for Britain at the Olympic Games and for me I don’t know whether that is the 10,000m or the marathon, because at the moment I’ve got qualifying times in both.

"So this is an opportunity to see what I can achieve.”

With the 2019 men’s wheelchair champion, Daniel Romanchuk, unable to defend his title the attention is focusing on two men who know what it is like to win in the capital - if not on a looped 1.3-mile course - in Britain's David Weir and Switzerland’s Marcel Hug.

The latter, who succeeded Weir as Paralympic marathon champion at the Rio 2016 Paralympics, won the London title in 2014 and 2017 and has been the only man to have beaten Romanchuk in the last 18 months, something he achieved by finishing ahead of the 22-year-old American at last year’s Tokyo Marathon.

Given the presence of his compatriot Manuela Schär in the women’s race, where she will defend her title having won her last nine Abbott World Marathon Majors races, the chances of a Swiss double look good.

"Because of the way COVID has affected everyone’s training and racing you don’t know how people have been managing, so it’s going to be a surprise," Schär said.

"I am just going to have to focus on myself."

The wheelchair racing will follow the women’s and men’s elite races on Sunday, and will be televised live on the BBC.

There are forecasts of rain - although it is likely to brighten up as the day goes on.

Weir, 41, is looking forward to seeking a ninth title in what will be his 21^st London Marathon title.

"I got a new wheelchair in May and it’s made a massive difference to me," he said.

"As soon as I got into it I felt alive again.

"It’s an aluminium chair, and although it probably won’t look any different to my previous one for me it just feels amazing.

"To be honest, with the flat course, I think it could be a sprinter’s race on Sunday - you’ve got to watch out for everyone."