Asked to comment, Wu replied in an email, "Not at this time — we are still under the Court's gag order."
The shift in defense counsel would be at least the third for Gates, 45, since he and his former employer, Manafort, 68, were indicted Oct. 30 on fraud, conspiracy and money laundering counts in the first disclosed charges in Mueller's probe of Russian influence in U.S. political affairs.
Both men have pleaded not guilty to the charges, which arose out of Manafort's secret lobbying for a Russia-friendly political party in Ukraine.
After the indictment, Gates replaced his initial attorney, Michael Dry, with Mack, of Doar Rieck Kaley & Mack in New York; Wu, of Wu, Grohovsky & Whipple in Washington; and McAvoy, a former federal prosecutor and consultant specializing in financial crime investigations.
CNN reported Jan. 23 that Gates had added white-collar lawyer Thomas C. Green of the Sidley law firm in Washington to his defense team, after Green was spotted at Mueller's office, fueling speculation about ongoing negotiations with prosecutors.
Green did not respond to requests for comment Thursday.
The timing of the change comes as the prosecution enters a new phase preparing for trial.
Gates last month reached bail terms on a nearly $5 million secured bond to gain conditional release from home detention, and prosecutors have turned over 640,000 pieces of evidence as the judge sets deadlines for motions challenging the indictment, before scheduling a possible fall trial date.
Manafort has yet to reach a bond deal and has individually filed a lawsuit challenging his indictment and Mueller's appointment as special counsel.
Correction: An earlier version of this report misidentified lawyer Michael Dry as George Dry.