The two-time Olympic gold medal winner, three-weight world champion and two-weight undisputed champion calls herself the 'GWOAT' - Greatest Woman of All Time - and has a strong claim to be women's boxing's No 1.
But she is switching sports to mixed martial arts to fight Brittney Elkin and tells Sky Sports about relocating to New Mexico, a hub of MMA, to train alongside UFC great Jon Jones and pioneer Holly Holm.
Describe the first time you felt how painful MMA could be…
It happened the first time I sparred. I got taken down and thought: 'Oh, this is what it feels like!'
I thought: 'It isn't that bad'.
I am avoiding being taken down, working my way back up from the cage, owning the centre of the cage with my punching.
I have put the work in and now things are coming to me easier.
I can kick, I can knee. I got stick for my footwork in boxing for only coming forwards aggressively but I've always had footwork. I could get in the ring and bounce around like Muhammad Ali. You will see my angles in MMA.
The girl I'm fighting is a brown belt in jiu-jitsu so we don't want to play her game, we want to play my game.
How important is it having Holly Holm in your gym?
She is well-rounded - she can kick, wrestle, grapple, she's tough. I look at her as my mentor.
I heard Kayla Harrison call herself my mentor but that's not true. Holly is my mentor.
I discuss my sparring and have real conversations with Holly. She is the only boxer to come into MMA and have real success.
She has the cheat code.
Does Jon Jones give valuable advice?
For four hours we just drill. The coaches sit back and watch him teach. They say: 'We hate to break this up but it's been four hours!'
Jon said: 'Claressa, let's go some more!'
Jon shows me things and will say: 'It will take you 30 minutes to understand this'.
People talk about his physical attributes but he is so technical. I can understand and catch on to what he teaches.
People expect you to fight world champions…
I don't let it add pressure. It's cool to be compared to those girls but Amanda Nunes, Cris Cyborg and Kayla Harrison have been doing MMA for years.
The only thing I have over them is my boxing.
I'm not thinking about those girls yet.
I text Cyborg to ask for advice. I'm cool with Kayla too but we fight [for Professional Fight League] so I can't call her! We are friends but we will fight one day so we have a disconnect.
After one year in MMA, you can't fight a world champion yet but I'm the exception.
People want to see me fight world champions. I learn very fast and not everybody possesses the skill that I do.
Why don't more boxers make this switch?
I trained five times - wrestling, cage work, jiu-jitsu, I did pads with my coach, I did kicking. It takes a while to put these things together.
Your mind has to understand. And you have to prepare the body - after wrestling, your arms are tired so don't want to punch.
That's why boxers don't come into MMA.
The WBO middleweight champion is on a collision course Shields inside the boxing ring...
Marshall said: It's a good move for her. Women's MMA, in my view, is on par with men's MMA.
If she reaps the benefits she may be tempted to stay in MMA.
It's a different level of fitness. She seems professional so she won't leave any stone unturned.
There are no easy fights in MMA, there are no journeywomen or padded records. You never see a champion in MMA with no losses.
She will be thrown into the deep end.