Next year's Paralympics need to be able to guarantee zero coronavirus cases, the head of the Games has told AFP, adding that they cannot go ahead if protection measures don't improve.
The warning from International Paralympic Committee president Andrew Parsons comes as Tokyo marks exactly one year to the postponed Games on Monday, with the pandemic still raging worldwide.
Parsons said some para-athletes were particularly vulnerable to the coronavirus, and that at current risk levels the Paralympics could not take place.
"If the situation was like it is today... if we were going to start tomorrow, we could not go ahead," Parsons said in an interview. "We need to learn more, prepare better."
After a recent surge in coronavirus cases, Tokyo is skipping the sort of public events held in 2019 to mark one year before the Games' original start date.
The unprecedented decision to delay the Olympics and Paralympics over the pandemic has created a logistical nightmare for organisers, and concerns remain over whether they can safely take place at all.
Parsons said current social distancing measures and standards for testing and tracing would not be enough to protect some 4,350 athletes plus staff and tens of thousands of fans, volunteers and media.
"We are not working with acceptable levels of risk. This is the bottom line, this is where we draw the line in the sand," he said.
"How we can ensure that we will not have one single case? One single case in the village can really disrupt the Games."
- 'Really severe, really fast' -
Exactly what measures will be necessary, and possible, remains to be seen.
Tokyo organisers and Olympic and Paralympic officials are expected to begin discussions next month on everything from quarantines to barring fans.
Parsons stopped short of saying he was optimistic that the Paralympics will go ahead, saying instead that he was "encouraged" by the restart of leagues such as US basketball's NBA.
But he acknowledged that the Games will be infinitely more complicated than other competitions, given their scale, number of events and international nature.
"This is why I'm saying, if we don't discover better ways of doing it, social distancing, monitoring, testing, it will be very difficult," Parsons said.
"What we need to have different from what the Olympic athletes have is not the protection to prevent them from being contaminated, it's what happens if they get contaminated, because it can be really severe, really fast," he added.
"The standard we have to take is, it doesn't matter if you have a disability or not. You don't get the virus, full stop."
Parsons also warned that the fallout from coronavirus posed a longer-term threat to para-sports, if government and sponsor support dwindles.
While top-level professional sport has made a tentative return from its coronavirus shutdown, athletes with disabilities face greater barriers to resuming training and competition.
The pandemic has "highlighted some inequalities around the world", he said, adding there were worries that "the focus of governments, or even media or even sponsor support will go only to these big leagues or athletes".
A poll of Japanese Paralympic athletes published Sunday by the Kyodo news agency found more than 70 percent are worried about training because of the coronavirus, though a majority also expressed hope that the Games would go ahead next year.
Parsons added that a lack of accessible and wheelchair-friendly accommodation in Tokyo remained a problem, and that there was likely to be a shortage of suitable hotel rooms.
He said the IPC was on alert to ensure that the cost-cutting measures necessary for a scaled-down, postponed Games did not involve lower standards of accessibility, which he called "non-negotiable".