Marshall defended her WBO middleweight title last weekend, which set up a potential megafight against Shields, and is trained by heavyweight champion Tyson Fury’s uncle, Peter Fury.
Shields currently holds the WBA, IBF, WBO and Ring Magazine belts in Marshall’s weight class.
That means a fight between the pair would crown an undisputed champion, a distinction Shields has achieved at light-middleweight and middleweight previously.
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Shields, 26, is widely regarded as the greatest female boxer ever having won two Olympic golds at London 2012 and Rio 2016 as an amateur – and then becoming a three-wright world champion as a professional.
The Michigan-born puncher, however, has been beaten just once in her entire ten-year career – against Marshall when the pair were both still in the amateur ranks.
That has lead to much speculation that the two will now meet in the professional game in a potential super fight.
"Nothing. Don’t believe the hype. She told everybody in the UK I retired from boxing to run away from her. No. I’m just so great, I can do MMA at the same damn time.
"I’m going to knock Savannah Marshall out. Sleep. Cold. She knows that. I’m a nine-time world champion, she just won a belt that became vacant because I haven’t fought in a year.
"She could have fought me for all the belts to prove what she’s saying but instead she waited for my belt to become vacant and then fought for the vacant title when she could have fought me, so no, she’s not ranked.
"She’s not ranked until she’s fought a Hannah Gabriel, or beat a Christina Hammer, beat somebody who is a world champion and not just brag about going ten rounds with Hannah Rankin, big whoop, congrats.
"You look at her resume, Hannah Rankin was her toughest test but everyone else gets two weeks' notice - she’s not fought anyone [else] who has a winning record.”