Gates and longtime business partner Paul Manafort - the chair of then-candidate Trump's campaign between June and August 2016 - were indicted in October 2017 by Mueller.
Trump's legal team and the special counsel have been at a standstill on the issue of an in-person interview for around five weeks, CNN reports.
Special counsel Robert Mueller has filed a heavily-redacted court document Tuesday afternoon outlining the underlying evidence to support its claims that Paul Manafort, the president's onetime campaign chairman, lied to federal investigators.
Gates was a star witness over the summer in a high-profile trial of Manafort, after he had pleaded guilty to lying to the Federal Bureau of Investigation and conspiracy against the United States in Mueller's probe in exchange for agreeing to cooperate with prosecutors under a deal that could lead to a reduced sentence.
If confirmed, that would indicate that the pair were doing so while Manafort was working for Trump's campaign and Russian Federation was allegedly interfering in the 2016 election to help his candidate win. But prosecutors have indicated Gates' cooperation has been wide-ranging, noting a year ago that his more than 20 meetings with prosecutors weren't confined to his work for Manafort.
Special Counsel Robert Mueller and lawyers for Rick Gates agreed to delay the former Manafort associate's sentencing date for the second time Tuesday.
At least four USA troops killed in Syria blast claimed by Isis
Since then, United States officials and Trump himself have suggested the withdrawal would be slower than initially thought . President Donald Trump said the group had been defeated there and that he would pull out all American forces.
"Mr. Manafort provided complete and truthful information to the best of his ability", his defense team wrote.
Also included in the January 15 filing were allegations from Mueller's team that Manafort lied when he said he had not communicated with members of Trump's administration after the president's inauguration. That was part of a deal in which Manafort escaped a trial on conspiracy charges past year in Washington, D.C.
Manafort's lawyers say any incorrect statements were inadvertent and that he has given the government valuable information.
Prosecutors filed a 31-page affidavit from an FBI agent, plus another 406 almost fully blacked-out exhibits, after a federal judge last week ordered them to lay out the "factual and evidentiary basis" for their claims that Manafort lied repeatedly after his plea deal and has breached his cooperation agreement. Details of those "various accounts" are redacted, but suggest he repeatedly changed his testimony over the course of several meetings with Mueller's team and a federal grand jury.
In addition to the polling data revelation, the filing also showed that Mueller believed Manafort lied to prosecutors about his discussions with Kilimnik on a "Ukrainian peace plan" and a previously undisclosed meeting between Manafort and Kilimnik in Madrid. The source of the funds is blacked out in documents. A sentencing date, in that case, has been set for February 8. Trump has praised what he called Manafort's toughness and unwillingness to "break."