A leading Tokyo 2020 Olympics official has called for the Games to be scrapped, if further delays are called for.
Last month, the International Olympic Committee and Japanese government postponed the Games until July 2021, because of the coronavirus outbreak.
But Tokyo 2020 president Yoshiro Mori has told Nikkan Sports, if the global recovery from COVID-19 eats into the new date, the Games need to be cancelled.
"In that case, the Olympics will be scrapped," Mori says. "Japan Medical Association chief [JMA] Yoshitake Yokokura told a media briefing earlier this week, it would be a big call for the Games to go ahead without a vaccine.
"I am not saying that Japan should or shouldn't host the Olympics, but that it would be difficult to do so," he says.
"Unless an effective vaccine is developed, I expect hosting the Olympics will be difficult."
Regardless, former Prime Minister Mori remains confident they will go ahead in 2021.
"We have delayed the Olympics until next summer, after we will have won the battle," he is quoted as saying.
"The Olympics would be much more valuable than any Olympics in the past, if we could go ahead with it, after winning this battle. We have to believe this, otherwise our hard work and efforts will not be rewarded."
Asked about Mori's comments, Tokyo 2020 spokesman Masa Takaya has emphasised organisers are focusing on next year.
"New dates for the Tokyo 2020 Games have been set and our mission is to deliver the Games next year," he has told a news briefing.
Mori "mentioned this comment in his own thoughts", Takaya adds.
During the interview, Mori also suggests the Olympics and Paralympics might share opening and closing ceremonies, instead of holding their usual separate ones.
Mori says this would cut costs, although the idea is further complicated by tickets already being sold for all four ceremonies.
"It's a big hurdle," he admits. "But due to the impact of coronavirus, the situation next year will be completely different... we have to review key areas, including the ceremonies."