Then-executive Producer and host Donald Trump (C) speaks about the NBC television show "The Celebrity Apprentice" during the TCA presentations in Pasadena, California, Jan. 16, 2015. Reuters

Donald Trump has urged black voters to back his campaign, saying, "What do you have to lose?" But his efforts to win over the crucial swing state voting demographic may have hit a roadblock Sunday after rumors leaked that Trump had used a racial slur while working as the host of the NBC reality show "The Apprentice."

Reporters have tried to find the unaired footage, while Mark Burnett, the television producer behind the show and a friend to Trump, has allegedly warned staffers not to leak the video, BuzzFeed News reported Sunday. The Associated Press reported last week that Trump made sexist remarks while hosting the show, but the unaired footage could prove more explosive, according to Bill Pruitt, a reality television producer who worked on “The Apprentice.”

"As a producer on seasons 1 & 2 of #theapprentice I assure you: when it comes to the #trumptapes there are far worse,” he tweeted.

Chris Nee, an award-winning screenwriter and producer, tweeted Sunday that she once signed a contract that said she would have to pay $5 million if she released footage from the show without Burnett's permission. She said the footage would show Trump using a racial slur to describe black people. Nee tweeted: "Hearing from producers/crew N word is the ‘much worse.'"

NBC said it could not release the tapes because it doesn't own the footage. "We're pursuing it along with every other news organization reporting on this story," an NBC spokeswoman told POLITICO.

Burnett has refused to released the footage, an unnamed source told BuzzFeed News. Burnett "is pro-Trump and has made clear to his teams that he will sue anyone who leaks," the person said.

The head of a pro-Clinton SuperPAC has vowed to cover the legal expenses of staffers on the show who release the unaired footage of Trump. "If a $5 million ‘leak fee’ is what stands between truth and total Trump implosion, sign me up," said David Brock, the founder of American Bridge, in an email to BuzzFeed News.

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The Washington Post released video Friday that included an unedited 2005 conversation between Trump and then-"Access Hollywood" host Billy Bush. "Grab them by the p---y," Trump tells Bush in the video as they discuss women. "You can do anything."

Several Republicans, including Arizona Sen. John McCain, have denounced Trump's remarks. A public opinion poll by POLITICO/Morning Consult found 39 percent of voters said Trump should drop out, and 45 percent said he should stay.

Trump said in a video statement early Saturday that the remarks "don't reflect who I am. I said it, I was wrong, and I apologize." He also attacked Democratic rival Hillary Clinton, accusing her of having "bullied, attacked, shamed and intimidated" her husband's "victims."

"I’ve said some foolish things, but there’s a big difference between the words and actions of other people," Trump said. "Bill Clinton has actually abused women ... We will discuss this more in the coming days."

In August, Trump told black voters to vote for him. He said: "You're living in poverty, your schools are no good, you have no jobs, 58 percent of your youth is unemployed -- what the hell do you have to lose?"