Fox News Channel chairman and CEO Roger Ailes has been adamant that network anchor Megyn Kelly will remain as moderator of Thursday's scheduled Republican presidential debate on the network -- even as GOP front-runner Donald Trump has pushed back against the decision.

Trump on Tuesday gave Ailes an ultimatum: Either Kelly's out as moderator, or he walks. 

"Megyn Kelly is an excellent journalist, and the entire network stands behind her," Ailes said in a statement Tuesday to Washington Post blog the Fix. "She will absolutely be on the debate stage on Thursday night."

Trump threatened Tuesday night to abandon his place on the debate stage, telling reporters in Marshalltown, Iowa, that he would probably not attend the Des Moines, Iowa, showdown.

"Most likely I’m not going to do the debate,” Trump said during a news conference. “I don't know what games Roger Ailes is playing.” Fox News Channel is Thursday's debate sponsor.

The games to which Trump was referring stem from a statement from a Fox network spokesperson in response to a social media poll Trump conducted hours earlier Tuesday.

"We learned from a secret back channel that the Ayatollah and Putin both intend to treat Donald Trump unfairly when they meet with him if he becomes president — a nefarious source tells us that Trump has his own secret plan to replace the Cabinet with his Twitter followers to see if he should even go to those meetings," the Fox statement said, CNN Money reported.

There has been ill will between Trump and Kelly since the first Republican debate in August, when the businessman denounced Kelly's line of questioning as unfair.

“Megyn Kelly’s really biased against me,” Trump says in an Instagram video posted Tuesday. “She knows that. I know that. Everybody knows that. Do you really think that she can be fair at a debate?”

If Trump walks, the network could risk losing viewership. The businessman has claimed full responsibility for Fox News' highest ratings in 20 years at the August debate. More than 24 million people tuned into watch Trump spar with the other Republican candidates.

Trump’s declaration comes as Fox News announced its lineup Tuesday. He was invited to appear on the main stage with Texas Sen. Ted Cruz, Florida Sen. Marco Rubio, retired neurosurgeon Dr. Ben Carson, former Florida Gov. Jeb Bush, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich and Kentucky Sen. Paul. 

Former Hewlett-Packard CEO Carly Fiorina, former Arkansas Gov. Mike Huckabee, former Pennsylvania Sen. Rick Santorum and former Virginia Gov. Jim Gilmore will appear at the so-called undercard debate for lower-polling candidates at 7 p.m. EST.

The prime-time showdown is scheduled for 9 p.m. Thursday EST on Fox News Channel.