Treasurer Scott Morrison has set himself in apparent opposition to Foreign Minister Julie Bishop over Australia’s nomination of Kevin Rudd as a candidate for secretary-general of the United Nations.

Cabinet is about to consider Rudd’s request for Australia to nominate him. Unless it does, he cannot run for the position, which he would have only an extremely outside chance of winning.

Bishop wants cabinet to agree to the nomination. She has told the government partyroom that “nomination” does not mean “endorsement”. Australia would risk criticism if it did not put forward the name of a former prime minister who is respected internationally.

Morrison invoked the case of Peter Costello in 2011, when he had made it “pretty clear that if there was interest in supporting him to be the new head of the IMF then he was interested”.

“He got nothing from Wayne Swan or Labor. Now the only difference between Peter Costello’s condition here and that of Kevin Rudd is that I think Peter Costello would be eminently qualified to take on that role,” Morrison said.

Costello never put himself forward formally for government support. When prime minister, Rudd took a bipartisan attitudes to overseas appointments.

On 2GB Ray Hadley asked Morrison: “And you are suggesting Mr Rudd is not eminently qualified to take on that role?”

Morrison replied: “You may well say that Ray … ”

“No I’m just interpreting what you said,” Hadley said.

“I couldn’t possibly comment. … we will have our views in cabinet about that,” Morrison said.

Prime Minister Malcolm Turnbull, asked whether Rudd had his confidence to lead the UN, played a dead bat. “The question about Australia nominating him to be secretary-general of the UN will be considered, as I have said many times, by the cabinet.”