Japan is the only logical choice for Super Rugby when the tournament expands into Asia in 2016, according to Eddie Jones.
Organisers SANZAR confirmed earlier this week that Japan and Singapore had tendered bids, but 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," Jones told AFP.
"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 ten 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 ten 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. Japan hosts the World Cup in 2019," he added.
"But professional rugby is all about money so there could be other economic factors."
SANZAR will make a decision in September or October.
The suggestion that Singapore could be selected in order to cut down on flying times for South African sides was given a 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? You have to take rugby to growth centres, not artificial places," he said.