Michael Avenatti is offering to fight Donald Trump Jr. in a three-round MMA fight for charity.

"I'm having lunch with Michael Avenatti ... at the Vanity Fair Summit and he's proposing a three-round mixed-martial arts fight with Donald Trump Jr ... for charity," senior media reporter for NBC News and MSNBC Dylan Byers wrote in a tweet Tuesday.

Avenatti, a frequent critic of the administration, replied, "This would be for two great causes. I'm in."

The Hill could not reach Trump Jr. for immediate comment on the offer at the time of publication.

Avenatti and Trump Jr. have clashed repeatedly over Twitter.

"Who else is excited about [Avenatti]/Weiner 2020?!?" Trump Jr. joked in a tweet on Monday, sharing the report that former Rep. Anthony Weiner (D-N.Y.) is expected to be released from federal prison early.

Weiner was sentenced to prison in September 2017 for sending sexually explicit messages to a minor, following the collapse of his political career when it emerged that he had sent pictures of his genitalia and lewd messages to multiple women.

"If I were you, the last thing I would be doing is referencing other people getting out of federal prison," fired back Avenatti, who has discussed trying to run for president as a Democrat in 2020.

"Because after you are indicted, you will likely be passing them on your way in. BTW, they don't have silver spoons or gold toilets in the joint. Buckle up Buttercup."

Trump Jr. attended the 2016 Trump Tower meeting in which members of the Trump campaign reportedly met with Russians tied to the Kremlin.

Trump Jr. has said he is "not worried" about jail time as a result of special counsel Robert Mueller's probe.