If the pandemic isn't done by 2021, the Tokyo Olympics will be cancelled.
Olympics chief Thomas Bach agreed 2021 was the "last option" for holding the delayed Tokyo Games on Thursday, stressing that postponement cannot go on forever.
Bach said he backs Japan's stance that the Games will have to be cancelled if the coronavirus pandemic isn't under control by next year.
In March, the Tokyo 2020 Olympics were postponed to July 23, 2021 over the coronavirus, which has killed hundreds of thousands around the world and halted international sport and travel.
"Quite frankly, I have some understanding for (Japan's position) because you cannot forever employ 3,000, or 5,000, people in an organising committee," Bach, president of the International Olympic Committee, told the BBC.
"You cannot every year change the entire sports schedule worldwide for all the major federations.
"You cannot have the athletes being in uncertainty, you cannot have so much overlapping with a future Olympic Games."
The IOC leader said it was a "mammoth task" to reorganise the Olympics, which have never been cancelled outside of the world wars.
Japanese officials have been clear that they have no intention of postponing the Games again beyond next year.
Bach warned "nobody knows" how the situation will play out, but said the IOC will act on advice from the World Health Organization.
"We have established one principle, and this is to organise these Games in a safe environment for all the participants," he said.
"Nobody knows what the world will look like in one year and two months from today, so we have to rely on (the experts)."
The IOC has already set aside $800 million to help organisers and sports federations meet the extra costs of a postponed Olympics.
According to the latest budget, the Games were due to cost $12.6 billion, shared between the organising committee, the government of Japan and Tokyo city.
© Agence France-Presse