NEW YORK -- CNN snapped up former Donald Trump campaign manager Corey Lewandowski three days after he was fired, and he began his new career as a political commentator Thursday by not answering a direct question about whether he'd agreed not to disparage his former boss.

Lewandowski made his first appearance on Erin Burnett's "Outfront" program Thursday evening.

He joins a stable of political commentators on a network that is covering the presidential campaign intensely. CNN has used a handful of Trump surrogates in its coverage, most prominently Jeffrey Lord and Kaleigh McEnany.

The Associated Press has reported that Trump requires nearly everyone working in his businesses and presidential campaign to sign nondisclosure agreements preventing them from releasing confidential or disparaging information about him.

Interviewed by Burnett, Lewandowski said he had agreed not to release confidential information. But when asked directly whether he had agreed not to "demean or disparage" Trump or his family, Lewandowski would not say.

"I'm a guy who calls balls and strikes," he said. "That's what I've done my entire career. That's not going to change."

Burnett asked Lewandowski whether, upon three days of reflection, he felt angry about his firing.

"I don't," he said. "I feel honoured to have been part of changing the American political system for the rest of our lives and hopefully so much further. The Trump family has been so good to me and my family and so generous that it's been so humbling to know that for a small period of time I had a small role in helping this campaign."

He said Trump was the only person who was going to save the country.

"Certainly nothing disparaging there," Burnett said.

Lewandowski also defended Trump for alleging that foreign governments had hacked into Hillary Clinton's email server when she was secretary of state, even as the candidate, under questioning by NBC News' Lester Holt, could not provide any proof of his accusation.

"You have to raise an issue," he said.

The combative Lewandowski joins a press corps that he was occasionally at odds with during the Trump campaign. That includes a CNN producer: Noah Gray tweeted last November that Lewandowski had threatened to pull his credentials when he tried to film a demonstration at a Trump rally.

Lewandowski also was charged with misdemeanour battery last spring following an altercation with a female reporter from Breitbart News who had tried to ask Trump a question following a rally. The charges were later dropped.

After his firing on Monday, he gave interviews to a number of reporters and remained positive toward Trump, saying he did not understand why he was fired. The campaign let him go following a rough three weeks for the presumptive Republican nominee.

Before signing with CNN, Lewandowski met with executives at MSNBC about a possible job there but the network decided not to hire him, said an NBC News executive who spoke under condition of anonymity to discuss a personnel issue.

Trump, meanwhile, tweeted two disparaging messages about CNN on Thursday, forwarding Breitbart News articles critical of the network. "The Clinton News Network is losing all credibility," Trump tweeted. "I'm not watching it much anymore."

The Lewandowski hiring was first reported by Politico.