Jake Paul has slammed Claressa Shields as "fake" and called her first MMA loss "karma" after she criticised him in the lead-up to her fight.

The world champion boxer is considered one of the best fighters in the world, and made the switch to MMA to test her skills as she waits for a fight with Savannah Marshall next year.

She won her PFL debut against Brittney Elkin earlier this year, but she was beaten by split-decision last night when she took on Abby Montes.

Montes was comprehensively and brutally out-struck on the feet by Shields, but when the fight went to the ground, the boxer's limited ability with wrestling and jiu-jitsu became evident.

And after a second batch of criticism towards the social media sensation in the lead up to this week's fight, Paul has hit back with a brutal put-down to his millions of followers.

"The truth hurts but it's necessary," Paul said. "Clarissa [sic] Shields is a loser. In MMA and even more so with her prima-donna attitude.

Claressa Shields was beaten by Abby Montes in her second MMA fight last night (


Cooper Neill/PFL MMA)

"The fake always gets exposed."

He compared the boxing star, who is still unbeaten and undisputed at light welterweight in her primary sport, to Conor McGregor and Ronda Rousey, who both suffered high profile defeats at the height of their fame.

Rousey infamously was knocked out by Holly Holm and later Amanda Nunes, while McGregor has been beaten by Nate Diaz, Khabib Nurmagomedov and Dustin Poirier twice during his UFC career.

"Losses come when anger and hate take over," he continued. "Just ask Ronda Rousey and Conor McGregor.

"She spent more time berating Jake Paul than learning jiu-jitsu, She's never been a big draw and unfortunately for her she never will be."

And Paul, never one to miss a chance to promote his business interests, used the message to remind followers that his fighter Amanda Serrano is in fact the 'GWOAT', or 'Greatest Woman Of All Time'.

Serrano is signed to his Most Valuable Promotions, and is expected to fight in the co-main event of his bout with Tommy Fury in December before taking on Katie Taylor next year.

"Amanda Serrano though, has 30 KOs in 42 fights," Paul concluded. "[She is] 2-0 in MMA, both wins by submission.

"Congratulations Abigail Montes on the win."

Shields' feud with Paul began during the build-up to the Montes fight, when she took great offence to being asked if she would ever fight on the same card as the YouTuber.

“I would never fight on the undercard of someone who does not possess the skills or accomplishments that I have," she said of Paul at the pre-fight press conference.

And the rivalry got more heated this week during the build up, when she declared that he was a "regular Joe" and promised that she would beat him one-handed in a sparring session.

"I don't know what world people live in that they think a man [could beat me] who has not been to the Olympics," she said. "Who has not fought professionally.

"There are a lot of women in boxing who could [out-box] men, especially a regular joe like Jake Paul!

"I know it's too much to fight him because it would be too embarrassing [for him], but if I were to spar Jake, I could use one hand.

"Just my jab, I wouldn't even have to use the banger.

"Just my jab - I would out-jab, out-hook and out-uppercut him. I would embarrass him."

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