Former Deputy FBI Director Andrew McCabe is seeking immunity in exchange for his testimony related to the Hillary Clinton email probe, something Fox News senior judicial analyst Judge Andrew Napolitano said is "very, very unusual."

An attorney representing McCabe on Tuesday sent a letter to Senate Judiciary Committee Chairman Chuck Grassley (R-Iowa) requesting that McCabe be granted immunity in exchange for testimony surrounding the inspector general’s report that he leaked information about the Clinton investigation to the press and lied about it to former FBI Director James Comey.

"I have to tell you, it's unheard of for the number two person at the FBI saying, 'You want me to testify? Give me immunity,'" Napolitano said on "Fox & Friends First" on Wednesday.

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He added that it's uncommon to seek immunity by writing a public letter, and these negotiations typically happen quietly behind the scenes.

"Giving immunity is so extreme, so unheard of, in this environment, so volatile, I can't imagine it happening," Napolitano said.

He said if McCabe privately tells Senate investigators what he knows and is willing to say under oath, they may find an immunity deal tempting, but he thinks that's unlikely.

"I don't think there's an appetite in Congress to grant this guy immunity. He is so disliked by Republicans, I just don't see it happening."

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