Mayor de Blasio’s aides are scared stiff about his impending interview with federal prosecutors in Manhattan over his fund-raising operation, a City Hall source said.

“Folks in the mayor’s office are very nervous about the mayor going in and speaking,” the source said. “Everybody is expendable.”

City Hall aides believe “someone is going to be sacrificed,” the source said.

“It’s tough to see how the mayor walks in there, turns to [US Attorney Preet Bharara], and says, ‘I’m innocent. I did nothing wrong. My staff is innocent. They did nothing wrong,’ ” the source explained. “He’s got to give them something.”

De Blasio agreed to the interview after Bharara convened a grand jury in December to look into whether he and his team gave favors to donors for their contributions to his 2013 campaign and his nonprofit, Campaign for One New York.

He answered state prosecutors’ questions on Jan. 25 in a separate probe of whether Team de Blasio broke election law when it funneled money through upstate county committees to help Democrats win the state Senate in 2014.

A cloud of suspicion has hovered over City Hall since April, when The Post reported that the FBI grilled about 20 cops over gifts and trips they allegedly received from de Blasio donors Jona Rechnitz and Jeremy Reichberg in exchange for favors such as providing police escorts.

Since then, federal and state prosecutors have widened their inquiries to business leaders, lobbyists, city employees and campaign workers to see if the mayor was engaging in pay-to-play schemes.

State prosecutors in November and December met with campaign fund-raiser Ross Offinger, top political aide Emma Wolfe, union political operative Josh Gold, and political consultants Bill Hyers and Hayley Prim of Hilltop Public Solutions to answer questions, according to a second political source.

BerlinRosen, a political p.r. firm helmed by top de Blasio confidant Jonathan Rosen, received a subpoena in connection with the investigation last April, but it has denied wrongdoing.

Another top mayoral liaison, Avi Fink, met with federal prosecutors regarding the donors and development projects, the source said.

The inquiry included the city’s lifting of deed restrictions on a Lower East Side nursing home. The move had allowed the Allure Group, whose executives had met with Fink, to sell the building to developers at a $72 million profit.

The mayor has quietly slowed down his introduction of new proposals while waiting for the inquiries to wrap up, the City Hall source said.

“A lot of housing policy and economic development projects have been frozen,” the source said. “He has been talking about past accomplishments instead of rolling out new projects because no one knows where they’re going to go.”

A de Blasio spokesman said it was “not true” that employees were anxious, and the mayor said on Friday that he would “fully cooperate” with prosecutors.