THERE are times when Savannah Marshall headed home from the gym wondering what on earth she'd let herself in for.

Hartlepool's undisputed super-middleweight world champion was the queen in the boxing ring but, at 33, stepped out from between the ropes and into the cage and the unknown.

On Saturday night, in Newcastle, Marshall will make her MMA debut at PFL Europe and she'll do as the headliner, against Brazilian Mirela Vargas.

Why the move? Well, her old rival Claressa Shields is one major factor behind the switch. We'll get to that. But also because boxing had very much been conquered. After unifying the super-middleweight division when she beat Franchon Crews-Dezurn in Manchester last year, and with Shields having already moved to MMA, Marshall had nowhere to turn. No real rivals. No mega fights. She needed a new challenge and a spark.

"The opportunity was too good to turn down," she says.

"I've accomplished everything I set out to accomplish in boxing. This is new, a new chapter."

But it's a new chapter which Marshall is happy to admit has been more challenging than she perhaps anticipated.

"Honestly, I'm quite embarrassed because I thought I'd walk into it and I'd be black belt and I'm getting tapped out by 15 year olds," she laughed.

"It's so humbling. There were times when I'd be driving home from the gym thinking what on earth have I let myself in for.

"I've had to have a beginner's crash course, a couple of years all rolled into nine months.

"It's a massive change. I see boxing as chess, especially at world level. Whereas although there's a lot of skill involved in MMA, it's like having a scrap!"

And a scrap is something Marshall will relish, especially if it's against her long-time rival Shields, which she hopes will happen in the not too distant future.

"I'd love that but at the minute I just have to get Saturday out the way," says Marshall, who has teamed up with the coach of interim UFC heavyweight champion Tom Aspinall to prepare for her MMA debut.

Shields, who is heading for Newcastle and will be cage-side on Saturday night, has fought once since her move back to MMA.

Dan Hardy, a former fighter and now MMA analyst and PFL's head of fighter operations, said: "This is massive. I can't stress enough the amount Savannah has had to learn and change to step into MMA. Even taking away the big gloves and taking the shoes off changes things.

"There are lots of fundamental things changing before we take into account wrestling and jujitsu. But Savannah has adjusted well. She's a really good student and has enjoyed learning and that gives me a lot of confidence. I think she's making more plans for her MMA career in the future than everyone else is and obviously she's gunning for that Claressa rematch.

"She's such a humble person that she can take all this in her stride. I think that's the mentality that will make her thrive in this sport."

Savannah Marshall fans can watch PFL Europe Newcastle at the Utilita Arena on 8 June from 5pm on DAZN.  Tickets are still available on Ticketmaster.