ABC News first reported about Monday's apparent meeting. Flynn resigned as national security adviser in February amid reports about previously undisclosed conversations he had with then-Russian Ambassador Sergey Kislyak.
Speculation about Flynn cooperating with Mueller's probe spiked last month when the special counsel hit former Trump campaign chairman Paul Manafort with an indictment that included money laundering allegations.
Flynn is facing federal, congressional, and military investigations into undisclosed payments from foreign governments, including Russian Federation and Turkey. He denied a request to appear before the Senate Intelligence Committee, and the Senate Judiciary Committee has sought information from the Justice Department about his resignation.
The visit comes on the heels of reports, confirmed by the president's attorneys, that Flynn's lawyers had stopped communicating with the president's legal team regarding the criminal investigation.
But one story buzzing over the weekend may end up being a watershed moment in this insane Trump era and that is the news that Michael Flynn's lawyers sent notice to the White House that they were withdrawing from an agreement to share information.
"I negotiated a cooperation deal for a target with Mueller's office when he was U.S. Atty and lemme tell ya, he's not gonna give one to Flynn unless he implicates someone up the ladder". Such agreements generally involve sharing information, "as long as the interests are aligned", he said.
Mateja said that given the report about the defense agreement, it is no surprise that Flynn's lawyers reportedly met with the special counsel team. "Stay tuned", he added, in a comment that was echoed by a former White House Special Counsel for Ethics who said Flynn would only be cooperating with Mueller if he had something on Trump.