Former ARU chief executive John O'Neill has urged Australia to do everything it can to ensure Japan hosts the 2019 World Cup amid fears the tournament will be taken away from them.
Japan's status as host nation has come under a cloud after World Rugby sought assurances about the successful delivery of the tournament following the loss of the new National Stadium as a venue.
It has been reported that Japanese Prime Minister Shinzo Abe has written to World Rugby chairman Bernard Lapasset to give his personal backing to Japan's World Cup. 
But O'Neill was concerned World Rugby's "ultimatum" to Japan would be a precursor to taking the World Cup away from the Japanese, who would be the first non-traditional rugby nation to host it.
"I've read the World Rugby press release regarding the assurances they are seeking from Japan and it concerns me that this ultimatum may well be a precursor to World Rugby stripping Japan of the hosting rights," O'Neill said.
"And indeed there has been some sentiment out of the UK in particular that the decision to award Japan the hosting rights in the first place was one that some would like to reverse.
"The fact is the ARU, New Zealand and other forward-thinking nations worked very hard to ensure Japan was awarded the rights to host 2019, being the first non-traditional territory to do so and being the first Asian country to do so and the strategic imperative is blindingly obvious that if World Rugby wants to live up to its objective of being a truly world game then every effort and every ounce of energy must be directed into ensuring Japan does host 2019.
"If you look at the composition of the organising committee that has been assembled, it is a very large collection of captains of industry in Japan, chairmen and CEOs of incredibly large and important companies across a range of industries.
"I have no doubt that these gentlemen will rise to the challenge as will the Japanese Government." Former ARU deputy chief executive Matt Carroll, who worked as the Japan Rugby union's interim chief operating officer in 2013, said the National Stadium was not part of Japan's bid to host the World Cup.
"I think it would be a very negative thing for rugby if the World Cup was taken away from Japan," Carroll said.
"The strategy of awarding the tournament to England was they knew they would make a lot of money, which is fine, and they could afford to be a bit more adventurous with the Japanese one and take a bit of a risk.
"The thing that seems to have started this is the decision of the Japanese government to delay the construction of the new National Stadium for the 2020 Olympics.
"What people have got to remember is that when Japan was awarded the tournament there was no new National Stadium. That only came onto the radar when Japan won the right to host the 2020 Olympics.
"The original bid had Yokohamo Stadium as the main stadium, so in actual fact nothing much has changed.
"Japan will get it done. The board is a who's who of Japanese business. I have no doubt they will stage a great World Cup." Asked whether Australia should bid for the 2019 World Cup if the tournament is taken away from Japan, O'Neill said: "I don't want to contemplate Japan falling over."Michael Hawker (ARU chairman) is on the board of Rugby World Cup. Australia should be doing everything it can to ensure Japan meets the assurances."