The mayor was seen leaving Gracie Mansion on Thursday morning, with no public schedule for the day.
Sources tell CBS2 that when the mayor does sit down with prosecutors it will be in his lawyer's Midtown offices for what is expected to be four hours of questioning.
As CBS2's political correspondent Marcia Kramer reported, the move may spare the mayor the embarrassment and media frenzy of having to walk into the U.S. Attorney's office, a picture no one running for re-election wants.
"It's very unusual. Usually with the federal prosecutors, if there's going to be a session with a potential target or a potential witness, it's in their office," Gerald Lefcourt, one of the city's top criminal defense attorneys, told Kramer.
Lefcourt said he's only seen prosecutors go to a private lawyer's office once in 35 years.
The federal probe is looking into whether the mayor and his aides gave favorable treatment to donors who contributed to his 2013 mayoral run. The donors in question reportedly include Harendra Singh and his city lease for the Water's Edge restaurant in Queens and real estate investor Jona Rechnitz.
"This is the biggest moment in his life. Certainly has to be very careful, but everything is on the line here, because obviously if he's charged with anything, that's the end of his career," Lefcourt said.
De Blasio has repeatedly denied any wrongdoing, saying everything was done with the advice of his legal team.
Still, with two grand juries taking testimony, it's unclear who called for the sit-down.
Kramer: "I just wondered if you asked for the meeting or did they?"
De Blasio: "We presented a willingness to cooperate from the beginning, and however the pieces came together, we're going to go in and have that meeting."
Legal experts say for the meeting to take place, the mayor's lawyers would have first hammered out a written agreement to set certain parameters. The agreement was reportedly the result of intense negotiations between the feds and de Blasio's lawyer, Barry Berke, who did not respond to a request for comment.
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