Mueller is looking at payments from Kremlin-backed broadcaster RT and transition contacts with former Russian Ambassador Sergei Kislyak, which led to his firing from the White House only 24 days after Trump became President.
Under the plan, Flynn, who was sacked by Trump after just 24 days in the job, and his son, Michael Flynn Jr, were to receive up to $15 million for forcibly removing Fethullah Gulen from his US home and delivering him to the Turkish government, people familiar with the investigation told the Journal.
Special counsel Robert Mueller is investigating an alleged plan in which former White House national security adviser Mike Flynn and his son, Michael Flynn Jr., were to be paid as much as $15 million in a plot to seize Muslim cleric Fethullah Gulen, who lives in the Poconos, and deliver him to Turkish officials, the Wall Street Journal reported, citing people familiar with the investigation. Gulen has denied any role in the coup.
The invitation, obtained by the newspaper, said the breakfast would "be a small event for about 50-60 guests" and that the White House chief of staff at the time, Reince Priebus, "might join the meeting", Daily Sabah reported.
Michael Flynn talks to media as he arrives with is son (l.) at Trump Tower on November 17, 2016.
The Journal said the people who described the alleged proposal didn't attend the December meeting and didn't have direct knowledge of the details. The group also discussed how to set free a Turkish-Iranian gold trader, Reza Zarrab.
Barry Coburn, a lawyer for Mr Flynn's son, told the BBC he had no comment on the report.
The sources could not confirm whether, in the meeting, Rohrabacher and Flynn discussed USA policy toward Russian Federation.
More: Michael Flynn faces legal peril in Washington. The well-compensated lobbying work Flynn Intel Group did for foreign governments has come under close scrutiny by Mueller's team.
Michael Flynn, the former national security adviser. Flynn then retroactively registered as a foreign agent. The very day Trump was elected, the retired lieutenant general published an op-ed in The Hill calling for the U.S.to not give "safe haven" to Gulen, whom he branded a "radical Islamist" - all without disclosing that he was being paid handsomely for this lobbying.
Robert Mueller, the special counsel investigating Russian manipulation of the 2016 U.S. election, has already indicted Trump's former campaign manager and another senior fundraiser on charges including money laundering and a former foreign policy adviser has pleaded guilty to perjury.