WASHINGTON, Sept. 13 (Xinhua) -- U.S. President Donald Trump's former campaign chairman Paul Manafort has tentatively agreed to a plea deal with Special Counsel Robert Mueller, according to media reports on Thursday.

The deal is expected to be announced Friday in federal court in Washington D.C., ahead of his second trial scheduled to begin later this month, said an ABC report, quoting sources familiar with the negotiation.

However, it remains unclear whether Manafort has agreed to cooperate with prosecutors or is simply conceding to a guilty plea, which would allow him to avoid the upcoming trial, according to the report.

A CNN report said though a deal was expected, its sources warned that the two sides have been close before.

Last month, Manafort was found guilty on eight out of 18 criminal charges of bank and tax fraud at the federal court in northern Virginia.

Five of the guilty verdicts were for filing false tax documents, and the other three involved foreign bank account registration and bank fraud.

These charges largely stem from Manafort's time working for a pro-Russian leader in Ukraine before the 2016 U.S. elections. However, the first trial did not specifically address any alleged collusion between Trump associates or officials and the Russian government.

A 69-year-old veteran lobbyist, Manafort joined Trump's campaign team in March 2016 and spent three months as Trump's campaign chairman until mid August 2016. Trump has repeatedly attacked the Mueller probe, saying it is a "rigged witch hunt."