After questioning the true amount of Donald Trump's "Apprentice" earnings, one TV personality couldn't put his money where his mouth is.

Following MSNBC host Lawrence O'Donnell's skepticism of Trump's reported NBC salary figures on Thursday morning, "The Apprentice" boss fired back with a proposal for him: Bet his entire salary on his assertion that Trump's financial claims are false.

O'Donnell quickly seemed to have a change of heart, giving an apologetic monologue on his show, "The Last Word," later that night.

"Now for a few words about Donald Trump. I like him … [At the White House Correspondents' Dinner] he spotted me, called my name. And watch what he did. He stretches out his hand for a handshake. That — he does that to a guy who savaged him four years ago when he was talking about running for president," O'Donnell said.

That came after the real estate mogul told O'Donnell that if he was so sure about the falsity of Trump's earnings, he should bet his entire annual salary on the claim.

"And today Donald came up with a better idea than threatening to sue me this time. He challenged me to bet 100 percent of my salary that I am wrong about his NBC income. Now where I come from, no one settled their disagreements with bets because none of us had any money to bet," O'Donnell said Thursday night.

O'Donnell's predicament arose after trading barbs Thursday morning with fellow MSNBC host Joe Scarborough on "Morning Joe" about Trump's NBC earnings. O'Donnell insinuated that Scarborough was being naive for believing the numbers that Trump reported. Then O'Donnell continued the spat over Twitter.

However, between Thursday morning and O'Donnell's show later that night, with Trump's bet laid down within that period, the personality made an abrupt about-face in his opinion.

"I don't want the prize for the guy who uses the meanest words in the debate. I don't want to be the angry guy about Donald Trump. Because I'm not," O'Donnell said.

He also made clear that despite his apparent admiration of Trump, he had no plans to take him up on his bet.

"So, no, Donald, there won't be any bet because I would never bet about anything … And, I might be wrong. I have never said I know exactly how much Donald Trump made for the entire series. I don't know. I've made semi-educated guesses about it and I don't really care very much about it … I stupidly jumped into talking about it again on 'Morning Joe' today where I, in effect, hijacked a few minutes of the show to talk about this thing that I know doesn't matter," O'Donnell said.

Trump called into "Morning Joe" Friday morning, evidently prepared to blast O'Donnell, but when he heard O'Donnell's apology, he immediately backed down from his planned attack.

"Well, I'm very disappointed because I was really all set to go after him this morning," Trump said. "And now I feel guilty if I do that. I feel very, very guilty. A lot of interesting things."