Bill de Blasio has cut off all contact with the man who was once both his top fundraiser and New York City’s top lobbyist, as corruption investigators probe whether campaign contributions to the mayor and his causes yielded improper favors.

The man, James Capalino, played a key lobbying role in the lifting of deed restrictions to allow real estate developers to flip a former AIDS hospice to luxury condos after paying the city $16 million — then reselling the building for a $72 million profit.

Documents released earlier in the week show that de Blasio and Capalino used to have direct contact, as Capalino did with de Blasio’s senior deputies, according to published reports.

“I have not been in touch with Mr. Capalino. He, going into the mayoralty, was someone that I respected and was a friend, someone I’d talked to a lot over the years, but I do not have contact with him anymore,” de Blasio said.

A message left with Capalino was not returned Tuesday.

De Blasio said he would have his press secretary, Eric Phillips, disclose when the mayor’s contact with Capalino stopped, but Phillips had not done so as of early Tuesday evening.

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Either the mayor or his inner circle are being investigated on a half dozen matters related to their fundraising methods, including the hospice, known as Rivington House, on Manhattan’s Lower East Side.

“I think in this atmosphere it’s absolutely sensible to have next to nothing to do with him,” de Blasio said, answering questions at an unrelated news conference about stopping unscrupulous landlords.

De Blasio said that he had changed his overall approach to dealing with the city’s lobbyists.

“I just have very, very, very, little contact with lobbyists,” he said.

Separately Tuesday, the city’s Conflicts of Interest Board announced that it had fined a former member of the Water Board, Joseph Finnerty, $1,000 for sponsoring a birthday fundraiser for de Blasio at the same time as he was on the board. Finnerty has since quit the post. He couldn’t be reached for comment Tuesday. The city’s conflicts-of-interest law prohibits a person with “substantial policy discretion” from such fundraising.

De Blasio on Tuesday said “we’re gonna tighten that up.”

“I’m very sorry that happened,” de Blasio said. “He’s a good guy. He was trying to serve the city. It was just an honest mistake.”

Since the Rivington scandal broke in March, de Blasio has maintained that no donor got special treatment simply for giving money. Earlier this year, de Blasio promised to give out a list of donors who contributed money and didn’t get their way. The list has not been released.

“We are a very, very careful, scrupulous group of people,” he said Tuesday. “We’re very careful about everything we do.”