International Olympic Committee President Thomas Bach says he understands why the rescheduled Tokyo 2020 Games would have to be cancelled if it cannot take place next summer.
Local organisers have said they have no back-up plan after the event was postponed by a year because of the coronavirus crisis.
"You cannot forever employ 3,000 to 5,000 people in an organising committee," Bach told BBC Sport. "You cannot have the athletes being in uncertainty."
In a wide-ranging interview, Bach also:
- admitted the job of re-organising the Games was "a mammoth task"
- warned that the event would "definitely be different" with a focus on "essentials"
- would not be drawn on whether a vaccine for Covid-19 would be needed for the event to take place
- insisted staging the Games behind closed doors was "not what we want", but he needs more time to consider whether that was feasible
Bach said he hoped the first ever postponed Games, which are due to take place from 23 July to 8 August 2021, could prove "unique" and send "a message of solidarity among the entire world, coming for the first time together again, and celebrating the triumph over coronavirus".
"There is no blueprint for it so we have to reinvent the wheel day by day. It's very challenging and at the same time fascinating."
Will a vaccine be found?
Japan's Prime Minister Shinzo Abe has admitted it may be "difficult" to stage the Games if the country does not successfully contain the virus, and the head of the Japan Medical Association has suggested it depends on finding a vaccine.
When asked directly if he agreed, Bach said: "For this question, we are relying on the advice of the World Health Organisation.
"We have established one principle: to organise these Games in a safe environment for all the participants. Nobody knows what the world will look like in one year, in two months.
"So we have to rely on [experts] and then take the appropriate decision at the appropriate time based on this advice."
The 2022 Beijing Winter Olympics are due to take place in China just six months after the Tokyo Games, and Bach said that Prime Minister Abe had made it clear to him that, as far as Japan was concerned, next summer was "the last option".
"Quite frankly, I have some understanding for this, because you cannot forever employ 3,000, or 5,000, people in an Organising Committee," said Bach.
"You cannot every year change the entire sports schedule worldwide of all the major federations. You cannot have the athletes being in uncertainty.
"You cannot have so much overlapping with a future Olympic Games, so I have some understanding for this approach by our Japanese partners."
When asked how confident he was that the Games would go ahead, Bach said: "We have to be prepared for different scenarios. There is the clear commitment to having these games in July next year.
"At the same time, looking at the scenarios this may require towards the organisation, with regard to health measures, these maybe need quarantine for the athletes, for part of the athletes, for other participants.
"What could this mean for the life in an Olympic Village and so on? All these different scenarios are under consideration and this is why I'm saying it's a mammoth task, because there are so many different options that it's not easy to address them [now]. When we have a clear view on how the world will look on 23 July, 2021, then [we will] take the appropriate decisions."
The director general of the World Health Organisation (WHO), Tedros Adhanom Ghebreyesus, has said it is possible but "not easy" for 11,000 athletes from more than 200 teams to come together in Tokyo.
Japan has recorded more than 17,100 cases and 797 deaths from the pandemic, but the numbers of infections are falling sharply and it has been affected far less than some other countries.
Could the Games be staged behind closed doors?
If social distancing restrictions are still in force in Japan next summer, some have suggested the Games may have to be staged behind closed doors.
Bach said such a scenario remained "speculation".
"This is not what we want," he said. "Because the Olympic spirit is about also uniting the fans and this is what makes the Games so unique that they're in an Olympic Stadium, all the fans from all over the world are together.
"But when it then would come to the decision... I would ask you to give me some more time for consultation with the athletes, with the World Health Organisation, with the Japanese partners."
The IOC has set aside $800m (£654m) to help with the financial impact caused by the postponement of Tokyo 2020. The total additional cost to Japan has been estimated at between two and six billion dollars.
But Bach said there would also have to be cutbacks to the Games.
"They will definitely be different, and they have to be different," he said. "If we all have learned something during this crisis, [it is] to look to the essentials and not so much on the nice-to-have things.
"So this concentration on the essentials should be reflected in the organisation of these Games... there should be no taboo."
Why were the Games not postponed sooner?
Two months ago, Bach faced unprecedented criticism from athletes for not postponing the Games earlier.
"The developments were so fast that you could not know what would happen tomorrow," he said when asked if he would do anything differently now.
'To find the balance between the more optimistic experts, saying, 'wait, you still have time. It's still some months away. Let's see how it goes', and the others saying, 'this will be a total disaster - why don't you take this decision right now?' This was the challenge every day.
"And this had to be done in consultation with our Japanese partners, because we could have cancelled the Games alone, without them, and that would have been an easy decision in one way.
"We could have said, 'OK, this is it.' We would have got our money being paid by insurance. And we could have started to prepare for Paris [2024 Games]. But this was not a real option because this would have deprived the athletes of this unique Olympic experience."
Bach said he was "happy" last weekend to see the Bundesliga resume in his native Germany, even though fans were not present.
"I wish that now all the other sports are coming back," he said. "On the other hand, I was a little bit feeling for the players, how strange it must be for them, playing in these huge stadiums...
"So I hope now that is the first step. Sport has to respect the rules, like any other organisation and area of society. But that slowly, we can come back and then maybe lift these restrictions in a responsible way."
Bach appealed to governments around the world to do what they can to help sports deal with the financial crisis caused by the pandemic.
"There is, first of all, the contribution of sport to health, and everybody realises that we must concentrate more on health in in the in the future," he said.
"Secondly, sport makes the great contribution to the inclusivity of society... sport is the best glue for a society.
"And thirdly, sport is also a very important economic factor. We had a study that about 3% of all the jobs being offered in Europe are sports-related.
"And this is why we are urging the governments to honour and to acknowledge the role of sport, and to include them in their recovery programmes."