(Reuters) - A Washington lawyer and Fox News guest who was expected to join U.S. President Donald Trump’s legal team this week in the special counsel’s Russia probe has yet to be retained, another of Trump’s lawyers said on Friday.

U.S. President Donald Trump participates in an onstage interview with moderator Charlie Kirk, founder of Turning Point USA, during a youth forum titled Generation Next, at the White House in Washington, U.S. March 22, 2018. REUTERS/Jonathan Ernst

Joseph diGenova’s hiring is pending completion of a review of potential conflicts of interest that may arise from representation of other clients at his law firm, Trump lawyer Jay Sekulow said.

On Monday, Sekulow said diGenova would sign on this week to help Trump respond to special counsel Robert Mueller’s investigation into possible collusion between the Trump campaign and Russia in the 2016 presidential election.

Trump’s lead lawyer in the special counsel investigation, John Dowd, resigned on Thursday.

DiGenova has not responded to requests for comment.

His law firm, DiGenova Toensing, has represented Mark Corallo, a former spokesman for Trump’s legal team, and Sam Clovis, a former campaign aide. Sekulow said he had expected the review to be completed by today.

Corallo represented Trump’s outside lawyers until last summer, when he resigned during another legal team shake-up.

Since then, Corallo has spoken with Mueller about what he viewed as a false statement dictated by Trump from Air Force One about a June 2016 meeting at Trump Tower in New York City that included several Russians, according to a person familiar with the matter. That meeting was attended by Trump’s son, Donald Jr.

Clovis, a former Pentagon official, was a campaign supervisor who wrote “great work” in an email after Trump’s foreign policy advisor George Papadopoulos discussed efforts to broker a meeting between the campaign and Russian leaders.

Corallo told Reuters on Friday that he had signed a waiver of potential conflicts on Monday.

Clovis could not be reached for comment, but a person familiar with the matter said appropriate waivers had been signed.

The addition of diGenova may signal a more aggressive strategy by Trump’s legal team to discredit Mueller, although Sekulow said this week that the team would continue to cooperate with the special counsel.

Trump’s lawyers have been negotiating the terms of a possible interview for him with Mueller, sources have said.

DiGenova has appeared on Fox News accusing the Federal Bureau of Investigation and the U.S. Justice Department of trying to frame Trump with false charges of colluding with Russia during the campaign.

Trump has had trouble finding outside lawyers to assist him in the Russia probe.

Major firms such as Williams and Connolly and Gibson, Dunn & Crutcher have turned him down in the last year, citing conflicts, people familiar with the matter have told Reuters.

Trump representatives have reached out to some of those firms again, sources said.