Opposition Leader Bill Shorten has labelled the Government's controversial resettlement deal with Cambodia "pathetic" following confirmation that one of four refugees transferred under the $55 million pact has returned to Myanmar.

Three Iranians and the ethnic Rohingya man left Nauru in May and landed in Phnom Penh a month later.

Immigration Minister Peter Dutton confirmed the transfer today.

"I can say that of the four people that originally went to Cambodia, one of those people has decided voluntarily to return [home]," Mr Dutton said this morning.

"There are another two people who have volunteered to go from Nauru to Cambodia."

Mr Shorten described the scheme as "failed".

He said the Government needed to negotiate genuine regional resettlement with the "big nations of our region".

"The idea that this government is proposing to resettle refugees at about $10 million a pop is ludicrous," he said.

"Labor is up for beating the people smugglers, but we also want to make that people in Australia's care do have genuine regional resettlement."

The Cambodia Daily newspaper reported the man was scheduled to fly out of Cambodia on Sunday after asking to leave last month.

The Cambodian government reportedly said the man asked to go because he was homesick.

Tan Sovichea, from the Interior Ministry, told the newspaper the man had all required travel documents.

"He can go on his own; we aren't sending him," he said.

Australia is giving the Cambodian government $40 million in extra aid after it agreed to take refugees who tried to reach Australia by boat.

The Government is also paying $15.5 million to the International Organisation for Migration (IOM) to support the refugees who move there.

A spokesperson for the IOM said they could not discuss the man's circumstances.

"Unfortunately, IOM can't discuss the case due to confidentiality principles, as well as the direct request of the client," they said.

"He has specifically asked IOM not to make any statements to the media regarding his case."

A spokesman for the Immigration Minister also declined to comment when contacted by the ABC.

$55 million a very expensive plane ticket: Greens

Greens immigration spokeswoman Sarah Hanson-Young slammed the Australia-Cambodia arrangement as a waste of taxpayers' money.

"$55 million is a very expensive plane ticket for these four people simply to dump them back in the Asia-Pacific," Senator Hanson-Young said.

"The money that Australia has paid that country is a bribe so that people can simply be sent there and dumped there and so the Australian Government doesn't have to look after them," she said.

"This isn't a solution, this is a waste of money and unfortunately we're playing with the lives of refugees."

The group was taken to an Australian-funded villa after arriving in Phnom Penh in June and promised language training and other assistance.

The Government has previously said it was confident Cambodia would resettle more than the initial four, and has said negotiations are underway to find other countries that will take refugees.