Paul Manafort’s attorney on Monday asked a federal judge to allow an investigation into whether special counsel prosecutor Andrew Weissmann illegally leaked confidential grand jury testimony to the press.

Attorney Kevin Downing ask District Court Judge T.S. Ellis in Virginia to compel Special Counsel Robert Mueller to disclose what Mr. Weissmann said to the Associated Press before it wrote negative stories about the former Trump campaign manager and his business ties to a Russian oligarch.

Mr. Weissmann is a hard-driving courtroom combatant. Conservatives criticize him for being a Democratic Party donor who attended Hillary Clinton’s planned victory party in New York and cheered the Justice Department resistance to President Trump.

Mr. Downing is seeking an investigative hearing into press leaks that he said damaged his client in the eyes of prospective jurors. The special counsel brought an indictment accusing Mr. Manafort of laundering money from politicians in Ukraine and failing to pay federal income taxes.

Mr. Downing’s filing late Monday was a response to Mr. Weissmann’s previous filing. He said that news stories cited by the defendant were not sourced to secret grand jury testimony, as alleged. Mr. Weissmann also asked the judge not to permit Mr. Downing to interrogate Mr. Mueller’s attorneys, meaning himself as well.

Mr. Downing said that even though a story does not specifically quote grand jury testimony it is clear the information from those proceedings has ended up in news stories.

Said Mr. Downing, “A simple Google search of ‘Mr. Manafort and Special Counsel’ yields hundreds of articles almost uniformly negative to Mr. Manafort and often disclosing confidential and classified information. These articles routinely disclose the grand jury investigations of former Ukrainian President [Viktor] Yanukovych, Mr. Manafort and his political campaign activities in Ukraine, and purported counterintelligence surveillance of the defendant.”

When the Associated Press story ran in early 2017, Mr. Weissmann headed the Justice Department’s fraud division.

“Despite protestations from the Office of Special Counsel, it appears that an investigation into government leaks surrounding the counterintelligence investigation of the Trump campaign — as it pertains to Mr. Manafort — would involve a small number of current and former government officials,” Mr. Downing said.

Mr. Downing said his main suspect is Mr. Weissmann, whom he referred to as Mr. Mueller’s “lead attorney.”

“The focus on grand jury leaks is likewise limited, primarily concerning communications between the Special Counsel’s lead attorney and four reporters from the Associated Press,” he said. “It appears that this investigation would involve approximately nine DOJ employees, including attorneys and FBI agents. The primary basis for having this inquiry comes from the questions raised by the House Permanent Select Committee on Intelligence, and the reporting of freelance journalist, Sara Carter.”

The House Intelligence Committee sent a letter to Justice asking it to explain a meeting Mr. Weissmann conducted with reporters while fraud division chief.

“Indeed, it is hard to fathom how the Special Counsel contends Mr. Manafort’s claim is speculative when the chairman of the House Permanent Select Committee on Intelligence has asked the Department of Justice for information on the meeting that the lead prosecutor in this case conducted with news reporters last year,” Mr. Downing said.

Mr. Downing cited four specific Associated Press stories from March to June 2017 on Mr. Manafort that could only have come from prosecutors or the FBI.

Mr. Downing has argued that the Ukraine case against Mr. Manafort was basically dead inside Justice until Mr. Mueller was appointed and brought Mr. Weissmann in to prosecute the case.

Judge Ellis from the bench accused the Mueller team of going after Mr. Manafort for decade-old bank transactions as a way to get him to flip as a witness against President Trump.

Mr. Downing said the New York Times and CNN have falsely reported that Mr. Manafort talked with Russian government officials during the campaign, when in fact he did not and there is no evidence that he did.

“Not only is leaking classified information a felony, but it was also apparently intended to create the false public narrative that Mr. Manafort was colluding with Russian intelligence officials during the Trump presidential campaign,” Mr. Downing said. “This smear campaign may have in fact irreparably prejudiced the jury pool in violation of the defendant’s Constitutional rights.”

He added, “There is strong evidence that the highest-level FBI and intelligence officials authorized leaks to the press and, in fact, leaked themselves. The identified officials include former FBI Direct.

A spokesman for the special counsel declined to comment.