Update: 7:18PM Japan is the only logical choice for Super Rugby's expansion into Asia in 2016, the country's head coach Eddie Jones told AFP on Friday.
Super Rugby will expand from 15 teams to 18 in 2016, with the return of the Kings from South Africa's Eastern Cape and a team based in Argentina already previously confirmed.
Organisers SANZAR confirmed earlier this week that Japan and Singapore would battle to fill the final team and a decision will be made in September or October.
Jones insisted Super Rugby would lose credibility if they were to ignore Japan's application.
"In terms of growing the game you'd think they would choose Japan," said the former Wallabies coach. "Singapore has no rugby history at all. They would just be coming and plonking a team of Pacific islanders there.
"It can't be the right choice. That's just crazy."
Jones has guided Japan's "Brave Blossoms" to a record 10 successive wins, culminating in a 26-23 victory over Italy in Tokyo last month which saw the Asian champions break into the world's top 10 for the first time.
"Japan's 10th in the world, has the world's fourth biggest rugby playing population, the world's third biggest economy," said Jones. "Japan hosts the World Cup in 2019.
"But professional rugby is all about money so there could be other economic factors."
The suggestion that Singapore could be selected in order to cut down on flying times for South African sides was given short shrift by Jones, currently preparing his side for next year's World Cup in England.
"Just because it's 11 hours from South Africa?" he said. "You have to take rugby to growth centres, not artificial places."
SANZAR's decision has raised concerns the extra teams will dilute the competition's quality.
Coastal Sharks coach Jake White pined for a return to the old format, where all teams played home and away games over the season, rather than being divided into a conference format.
That view is not shared by Jones, who gave credit to football's ruling body FIFA for taking the World Cup to Asia for the first time in 2002.
"FIFA has been criticised for a lot of things but they've really managed to grow soccer," he said. "When they brought the 2002 World Cup to Japan and South Korea it really helped boost the game across Asia."