It was not clear which charges Manafort might plead guilty to or whether he would cooperate with Mueller's team in its investigation into Russian interference in the 2016 election, possible collusion with the Trump campaign and obstruction of justice by Trump.
Proceedings scheduled for September 17 would begin a second gruelling, expensive, politically explosive three-week-or-longer trial in federal court.
Spokesmen for special counsel Mueller and Manafort would not respond to requests for comment.
ABC reported Thursday that a tentative deal has been reached. He was previously reported to be resisting Mueller's demands for information relating to Trump in return for a deal. Another trial was to begin later this month based on charges filed against Manafort previous year in Washington, DC.
Giuliani - the most visible and outspoken lawyer representing Trump - also claimed to Politico that he and Manafort's attorneys are in regular contact, including before and after a jury in Virginia delivered its verdict in the federal trial Manafort faced there.
Rick Gates, Manafort's former business partner and the campaign's deputy chairman, pleaded guilty to lesser charges in exchange for his cooperation, later testifying against Manafort in Virginia. He resigned in August 2016 following a news report linking him to covert payments from a pro-Kremlin political party in Ukraine.
A CNN report said though a deal was expected, its sources warned that the two sides have been close before. A pretrial hearing, postponed this week, is scheduled for Friday.
Although most of Manafort's charges predate his work for the Trump campaign, his conviction was still considered a huge victory for Mueller's Russian investigation - which Trump has exceedingly bashed and decried as a "witch hunt."
Mr. Trump has repeatedly come to Mr. Manafort's defense.
A judge declared a mistrial on 10 other counts the jury could not agree on. In private discussions with his lawyers, Mr. Trump has raised the option of pardoning Mr. Manafort.