The postponed Tokyo Olympics will be "scrapped" if they cannot take place in 2021, says Games chief Yoshiro Mori.
Tokyo 2020 is now scheduled to run from 23 July to 8 August next year after being delayed because of the coronavirus pandemic.
Health experts have cast doubt on whether the Games could be held next summer without a vaccine or effective drugs to treat COVID-19 being found.
When asked if the event could be moved again to 2022, Mori replied: "No."
"In that case, the Olympics will be scrapped," he added.
The president of Japan's medical association, Yoshitake Yokokura, said on Tuesday it will be "difficult" to hold the Olympics in 2021 without vaccines or effective drugs being developed.
"I am not saying that Japan should or shouldn't host the Olympics, but that it would be difficult to do so," he said.
"If the infections are under control in Japan, it will still be difficult to hold the games unless the pandemic is over in the rest of the world."
Most experts think a vaccine is likely to become available by mid-2021, though others have warned there is no guarantee a vaccine can be successfully developed.