Australia have not signed the Rugby League World Cup participation agreement despite organisers confirming it will take place in England this autumn, says the tournament's chief.
The men's, women's and wheelchair events will all take place simultaneously in October and November.
Australia are holders of the men's and women's titles.
RLWC2021 chief executive Jon Dutton told BBC Radio 5 Live's Rugby League podcast Australia are yet to sign.
However, he added: "We are incredibly confident they will sign the agreement and send strong teams across all three competitions."
There are issues regarding Covid-19 regulations and quarantine rules for players and staff travelling back to Australia and New Zealand.
Australia's borders are currently closed, so anyone returning has to spend 14 days in government-managed quarantine.
There are reports that Australia's National Rugby League (NRL) teams want the tournament postponed to next year because those regulations mean players would only return to their clubs two weeks before trial games for the 2022 NRL season begin.
Rugby league officials estimate around 400-500 players, staff and team officials from NRL sides, representing several different countries, would be involved.
Dutton said RLWC2021 will continue to work with the Australian Rugby League Commission (ARLC) and are "respectful" of the challenges currently facing Australia and the NRL.
Sydney is in lockdown and 12 NRL teams have relocated to Queensland in a bio-secure bubble to ensure the 2021 season can be completed.
England are set to take on Samoa in the opening game of the men's tournament at Newcastle's St James' Park on 23 October.
"We've got a lot of work to do over the next 100 days," said Dutton, who added there is no deadline for Australia to sign.
"We will do it to the very best of our ability, we will be professional and respectful, but with that drive and determination to stage the best ever rugby league World Cup."
Dutton said cancellation and postponement to 2022 were options but the latter was "significantly unpalatable" with the men's football World Cup, the women's European Championships and the Commonwealth Games taking place next year.
He said there is "a contingency in place" if Australia do not agree to play and there are "a number of nations who would step up if any nation didn't take part for any reason across all three tournaments".
These issues have led to concerns Australia may field teams not featuring their strongest players.
Dutton said any "normal tournament" would have some of the sport's best athletes missing through "injury and other circumstances" and that the "pandemic has added to that".
"We've been speaking to players and we know what it means to them and we think that enormous pride from the players will shine through," he said.
"We think that will ensure the athletes will arrive. Will they all arrive? They clearly won't, but that's no different to any other tournament."
Wales head coach John Kear said it would not be "detrimental at all" if Australia did not send their strongest squad for the men's tournament and that they would still field a "very representative side" because of their strength in depth.
He added he expected players to "stand up to their clubs" and that while "there may be some clubs who don't release their players, Australia will still put a quality team out".
There will be 61 matches across the three tournaments, played at 21 venues, live across the BBC.
The men's final is set for 27 November in a double-header with the women's final at Manchester's Old Trafford.
The women's tournament is scheduled to start on 9 November and the wheelchair event is due to run from 11 November to 26 November.
Dutton said the event is a "seminal" and possibly "transformative" moment for the sport and they are ready to stage "a safe tournament and a celebration of rugby" that could also be a "celebration of humanity, for everything we've been through" with the pandemic.
"Some of the host towns and cities - St Helens, Warrington, Leigh - have been hit hardest in the pandemic but maybe would never stage a World Cup match in any other sport, so this is their moment to shine," he added.
"The men's European Championships unified the nation and we can do that on a national and global scale."
Kear said it "absolutely vital" the tournament goes ahead and it will "raise the nation's morale".
He added: "People will look back in 20 to 30 years' time and they'll see this was a significant piece of rugby league history."
Marking 100 days to the start of the tournament on Thursday, culture secretary Oliver Dowden said: "After the challenges of the past 18 months where the positive impact of Rugby League in communities has shone through, the moment when the men's, women's and wheelchair teams take to the pitch will be a watershed moment for both the sport and the country."
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