Alexander Downer sat down for an interview with two FBI agents in London in 2016 to discuss potential Russian meddling in the US presidential election, a sensational New York Times report alleges.
The revelation the Australian government broke with diplomatic protocol and allowed Mr Downer, then Australia's high commissioner to the United Kingdom, to be interviewed by the FBI could damage Australia's recently repaired relationship with US President Donald Trump.
The New York Times first revealed late last year it was at a boozy night in May 2016, at London's Kensington Wine Rooms, that Mr Trump's then foreign policy adviser George Papadopoulos told Mr Downer that Russia had dirt on Mr Trump's political rival Hillary Clinton.
"Within hours of opening an investigation into the Trump campaign's ties to Russia in the summer of 2016, the FBI dispatched a pair of agents to London on a mission so secretive that all but a handful of officials were kept in the dark," the New York Times reported on Wednesday.
"Their assignment, which has not been previously reported, was to meet the Australian ambassador, who had evidence that one of Donald J Trump's advisers knew in advance about Russian election meddling.
"After tense deliberations between Washington and Canberra, top Australian officials broke with diplomatic protocol and allowed the ambassador, Alexander Downer, to sit for an FBI interview to describe his meeting with the campaign adviser, George Papadopoulos."
The FBI agents summarised "their highly unusual interview" and their report helped provide the foundation for a case that became the probe headed by special counsel Robert Mueller, who is investigating allegations of collusion between the Trump campaign and Russia.
Mr Trump has repeatedly slammed the probe as a witch hunt.
Mr Papadopoulos became one of Mr Mueller's first scalps, pleading guilty to lying to officials.
He is co-operating with Mr Mueller's investigation.
The FBI codenamed their probe Crossfire Hurricane, a reference to lyrics in a Rolling Stones song.
Crossfire Hurricane began exactly 100 days before the November 8, 2016 presidential election won by Mr Trump.
Australian Prime Minister Malcolm Turnbull has carefully attempted to repair his relationship with Mr Trump after the leaders had a fiery phone call about a refugee deal a week after the president moved into the White House.
Foreign Minister Julie Bishop refused to confirm whether Mr Downer had been interviewed.
"These are matters of security and intelligence and I don't intend to go into them," Ms Bishop told reporters in Perth on Thursday.
But Ms Bishop said no-one in the administration had raised any concerns over the issue with her.
She did not believe it had damaged Mr Turnbull's relationship with Trump.