However, the rest of the delegation then travelled to the city of Izumisano for a planned pre-Olympic training camp, but without being identified as “close contacts” of the coach. Another delegation member also tested positive for Covid-19 on Wednesday.

The incident sparked concern among local governments planning to host Olympic delegations, with one governor saying they should be held at or near the airport if a member tested positive upon arrival.

“No matter what measures are put in place, there is no way we will have zero positive cases arriving,” Yamashita told reporters on Monday. “Even if you’ve had two vaccine doses, it doesn’t guarantee every individual will be negative.

“In order to make sure no clusters arise, we need to have thorough measures at the border at the time of entry to Japan,” Yamashita said, adding that daily virus testing would also help reduce the risk of infections spreading.

Yamashita, a former Olympic judo gold medallist, said he sympathised with the athletes, who will be confined to the village when they are not training or competing.

Athletes must sign a written pledge promising to abide by antivirus rules in Tokyo, including staying away from tourist areas, shops and bars, limiting contact with other people, and not using public transport.

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Yamashita said: “How can international athletes have some time to relax and create some positive memories? Of course, the top priority is to make it safe and secure, but I think we need to make an effort to give athletes that kind of space.”

Many Japanese remain sceptical about the possibility of safely holding even a scaled-down Games during the pandemic, which caused the event to be postponed last year.

In a poll of Tokyo residents published on Sunday by the Asahi newspaper, 38 per cent of respondents said it was best to host the Games as planned this year, while 27 per cent wanted a further delay and 33 per cent sought outright cancellation.

Organisers have excluded foreign spectators from the event and limited domestic numbers. Alcohol, high-fives and loud talking will also be banned.

Williams did not give a reason for her withdrawal, but a ban on family members at the Olympics would have separated her from her daughter.

Yamashita, who won gold at the 1984 Los Angeles Olympics but missed the 1980 Moscow Games because Japan boycotted the event, said athletes would find it “difficult” to spend so long cooped up inside.

“I think the athletes will be spending their time here in Japan in extremely restricted conditions,” he said. “I think this is something that we need to understand, and not think of the athletes as being strong-willed or selfish.”

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Yamashita lamented the fact that virus restrictions and a ban on overseas fans coming to Japan means the Tokyo Games will not be the cultural exchange he was looking forward to. But he hoped the event could still leave a meaningful legacy.

“There was a feeling that the Olympics were becoming huge and extravagant,” he said. “I believe we’ve been given an opportunity to rethink what the Olympics are about. I think that’s where the Tokyo Games can be significant.”

Additional reporting by Reuters