The former deputy chairman of the 2012 London Olympic organising committee said on Tuesday he would be planning for a cancellation if in charge of the Tokyo Games.
Keith Mills told BBC radio that the delayed Summer Games scheduled for July and August were looking unlikely to happen in his opinion due to the coronavirus pandemic.
"If I was sitting in the shoes of the organising committee in Tokyo, and thankfully I’m not, I would be making plans for a cancellation," he said.
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"I’m sure they have plans for a cancellation but I think they will leave it to absolutely the last minute in case the situation improves dramatically and in case the vaccines roll out faster.
"It’s a tough call and I wouldn’t like to be in their shoes."
Japanese Prime Minister Yoshihide Suga vowed on Monday to forge ahead with preparations for the Games in the face of growing public opposition as Japan battles a surge in coronavirus infections, while officials said $900 million would be spent on safety measures.
Recent media polls showed close to 80% of Japanese believe the Olympics, already postponed by a year because of the pandemic, should be delayed again or cancelled entirely.
Tokyo 2020 spokesman Masa Takaya played down the polls and said the Games would go ahead, with as many spectators as possible and even without vaccinations.
"Our position remains -- we will deliver the Games," he told BBC Scotland. "Our counter measures on Covid-19 are working under the assumption that we will not have a vaccine, so even if we do not, our plan is that we will be able to deliver the Games."
World Athletics head Seb Coe, who was the chairman of the 2012 organising committee, told Sky News he did not think the Games would be cancelled but they would be a challenge and a very different experience.
"Of all the countries on the planet that really has the fortitude, and resilience and the street-smarts to see this through, it is actually Japan," he said.

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"I wake up as a federation president really grateful that it is Japan that's dealing with this and not some other places that I can think of. So I'm sure we will be there.
"I think there will be big issues around crowds and distancing the athletes. Just think about the village, you've got 10,500 athletes and probably another 7,000 support staff in there and they're all probably wanting to eat at roughly the same time," he added.
"I think the Games will take place but they will look different."
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