7:35 PM ET

CLARESSA SHIELDS RETURNED to JacksonWink MMA in Albuquerque, New Mexico, in late March, fresh off making boxing history by becoming the first two-division undisputed champion in the four-belt era.

Time was running low, though, with Shields scheduled to make her MMA debut in the Professional Fighters League on June 10. The only way to get one of the world’s best female boxers ready for her first trip into the cage was to throw her into the deep end of the MMA pool to see if she would sink or swim.

In early April, Shields participated in her first mixed martial arts sparring session. She admitted she was “afraid” of it.

“Of course, fighting on the ground [was scary],” Shields told ESPN. “Not knowing how to get back up. Not knowing how to keep somebody from grabbing me or not being able to stop somebody from taking me down. Armbars and all of that kind of stuff.”

The goal for Shields in that sparring match with teammate Kayla Yontef was to stay standing as long as possible. Shields said Yontef took her down 15 to 20 times during that session. Such is the steep learning curve for a world-class fighter who really only started wrestling, grappling and throwing kicks when she arrived at JacksonWink MMA in early December.

Shields, a two-time Olympic gold medalist in boxing and a three-division boxing champion, said she feels much more comfortable on the ground now as compared to 10 weeks ago. But her strategy when she makes her MMA debut against Brittney Elkin, a brown belt in Brazilian jiu-jitsu who has won grappling titles, isn’t going to be a huge mystery.

“The game plan is to stay the f— away from the cage,” Shields said. “That’s it. Stay in the center.”

Shields’ coaches indicated she has improved dramatically — as fast as they have ever seen — ahead of her debut in the cage on Thursday in Atlantic City, New Jersey. Greg Jackson and Mike Winkeljohn, two of the top coaches in MMA history, not only believe Shields will do well as a beginner, they think she has a chance to be an all-time great in the sport if she continues to work at it. But it’s going to take a lot of work.

The first step toward that mountain of possibilities will be on Thursday.

SHIELDS AND UFC legend Jon Jones had been friends for several years — through social media interactions and seeing each other at fights — when they caught up at the ESPYS in the summer of 2018. Jones told Shields that if she ever wanted to try MMA, there would be a home for her with his team, JacksonWink MMA.

“I thought he was crazy,” Shields said. “I’m not even thinking about doing MMA; I don’t know why you’re offering me that.”

Her perspective changed dramatically over the course of the pandemic. Shields said being stuck in quarantine made her realize she wanted to make some changes in her life and career. The Flint, Michigan, native said she started to feel like she had done almost everything she wanted to accomplish in boxing, and despite her accolades, she wasn’t getting paid as much as male boxers. Shields said the most she made from a boxing fight was $350,000.

“I just got tired of it, because I was putting in so much hard work and so much time in the gym — putting in all this hard work to be dominant,” Shields said. “Putting in all this hard work to win. And it was just like, what’s my reward? Where’s my endorsement deals? Where’s my sponsorships? Where’s my million-dollar payday? Where’s the pay-per-views? I wasn’t getting those opportunities.”

Late in 2020, Shields’ manager, Mark Taffet, opened discussions with the PFL about Shields doing MMA. The 2021 PFL season features a women’s lightweight division for the second time, with the winner taking home $1 million after fighting through a regular season and a four-woman playoff bracket.

That became the goal. But Shields wanted to start slow, learning little by little and fighting opponents near her experience level in MMA early on. That’s why, at least for her first season of action in the PFL, Shields will be competing in showcase fights and not as part of the $1 million competition.

She’ll also continue to pursue boxing, at least for the time being, and it will be a balancing act. In addition to two scheduled fights in the PFL, Shields intends to take a boxing fight toward the end of 2021. There are still three or four opponents that Shields wants to defend her titles against in the sport that made her famous, but a significant chunk of her attention will be turned elsewhere.

“I’m really more just focused on MMA right now,” Shields said.

A FIGHTER WITH a résumé like the one Shields carries has the kind following and name recognition to book a lucrative fight that would far exceed her experience level — against MMA legends such as Amanda Nunes in the UFC or Cris Cyborg in Bellator. But Shields is serious about MMA as a career, and she wasn’t interested in simply cashing in on any kind of one-off event.

“Everybody knows I want to fight the best, but I’ll fight the best when I’m the best in MMA,” Shields said. “I don’t want to be taken advantage of and things of that nature. So, I want to get my training in and fight an opponent that’s equal to me in MMA. And then kind of build my way up from there.”

The decision to dive headfirst into MMA and dedicate herself to doing it the right way was crystallized when Shields took Jones up on his offer and flew down to Albuquerque in December to see if she liked the environment. She did, and she spent several weeks there before returning home to Michigan to prepare for her boxing title unification fight against Marie-Eve Dicaire.

When Shields returned to JacksonWink, rather than securing fancy accommodations, she moved into the dorms adjacent to the gym. She has a plush three-bedroom home with a full boxing gym in her basement in Michigan, but Shields wanted a place in Albuquerque with no frills and easy access to the gym.

Shields said she sometimes trains five times a day. The dorms, she said, remind her of the Olympic training center in Colorado, where she lived for two years during her amateur days.

“I kind of just wanted to feel like I’m working my way up from the bottom, even though I’m not completely at the bottom,” Shields said.

WHEN SHIELDS ARRIVED in Albuquerque, she didn’t even realize former UFC women’s bantamweight champion Holly Holm trained at JacksonWink. All Shields knew was what Jones had told her and the prominence of coaches Jackson and Winkeljohn. Holm was one of the top female boxers in the world before becoming a standout in MMA, one of the very best to have ever made that transition.

Since Shields’ arrival, Jones and Holm have become significant resources for Shields to tap into. Shields said she has sparred with Holm about five or six times, and Holm has shared her knowledge. Winkeljohn said Shields has had an even harder learning curve than Holm, because Holm was already an accomplished kickboxer prior to her venture into MMA — another element of MMA that Shields didn’t have to account for in a traditional boxing ring.

But Winkeljohn saw something in Shields right away. He said even though Shields was in over her head on the ground initially, she never quit. She kept fighting and trying to mount an offense.

“She didn’t know what she was doing, but she had that fighter attitude,” Winkeljohn said. “I love that about her.”

THE EFFORT TO get Shields ready to step into the cage is twofold, separating the useful elements of Shields’ boxing experience from what won’t work in MMA. On the feet, Winkeljohn said he has worked with Shields on not relying too heavily on the “Philly shell” or “shoulder roll” defensive technique used in boxing (keeping her left hand down). It’s too dangerous in MMA and leaves too many potential openings for opponents, Winkeljohn said. Jackson is the one tasked with turning the elite boxer into a fighter competent in wrestling, the clinch and the grappling game.

Beyond the X’s and O’s, Jackson said that Shields has something he calls the “Claressa computer,” an innate ability to make adjustments on the fly during a fight or even during a sequence. Jones, one of the greatest MMA fighters to ever live, has it, Jackson said, but “it’s not common at all.”

That ability has helped Shields tremendously as she tries to ingest and process a staggering amount of information and technique — and then put it all together for the first time in her pro debut. And while most debuts tend to take place outside the spotlight on a regional level, Shields’ first MMA fight will be the PFL’s main event during its broadcast on ESPN.

“Certainly, that’s the quickest I’ve ever seen anybody adjust to [those new skills],” Jackson said.

“I’d like everybody to understand just how brave it is what she’s doing. She had zero kickboxing, zero ground. Nothing. Just jumping in on a big stage in front of millions. It’s unprecedented courage, in my opinion.”

So what is the ceiling for someone who is getting better this quickly and has the smarts, the physical skills and a combat sports background? There isn’t much of one, Jackson said.

“All the way to the top, there’s no doubt,” he said.

AFTER GETTING TAKEN down more than a dozen times in her first sparring sessions, Shields said two weeks ago she was only getting taken down about twice per session. Jackson said Shields had an epiphany in recent weeks, after she got taken down and her first technique to try to get back up failed. Shields stuck with it, went through her reads and got up on her third technique.

“The light bulb was starting to come on, and that was really cool to see,” Jackson said.

Certainly, Shields doesn’t even want to end up on the mat. She is an elite boxer with power in her hands, which are sure to be even more dangerous in 4-ounce gloves, as compared to the 8-ounce or 10-ounce gloves she uses in boxing. Shields said she loves being on offense and wants to be like a bigger version of former UFC women’s strawweight champion Joanna Jedrzejczyk, mixing in a volume of kicks, knees and elbows with her punches.

“It’s fun,” Shields said of MMA. “But like I said, it’s very challenging. It’s not meant for everybody. You really have to be someone who loves fighting. You get kicked in the stomach and some people are like, ‘Oh, that s— hurts.’

“To me, it’s like, ‘Yeah, it hurts, but I’m gonna get my lick back. I’m gonna kick her back in the stomach. I’m gonna kick her head. I’m gonna punch her hard in the stomach.’ You’ve gotta have that certain mentality for MMA.”