Claressa Shields Offers To Train Sydney Sweeney For Charity Boxing Match

If Sydney Sweeney's serious about getting in the ring for a good cause, she could have one of the greatest women's boxers EVER in her corner -- 'cause Claressa Shields tells TMZ Sports she's down to train the actress for a charity boxing match!!

We caught up with the undisputed heavyweight champion out in NYC this week .. and she said every woman should lace up the gloves and throw some hands at least once.

It would make sense four Sweeney ... considering she just played Christy Martin in a new movie, and trained her ass off for the role. She teased this week she could really take a charity bout.

"I think every woman should experience one," Shields said. "Win, lose or draw. But if she played Christy Martin and I heard she did MMA back in her younger years ... hell, why not?"

"If she needs some help training, girl, call me! I give you some G.W.O.A.T. tips."

Grab a pen and paper, Sydney ... 'cause we were able to get some advice from the champ!!

"The jab is the most powerful punch in boxing and anybody that's stronger than you, you hit them in the stomach," she said. "Then they get weaker."

While Sydney didn't elaborate on whether or not headgear would be worn ... Shields made it clear there's no shame in wearing some protection.

"I think you do the no headgear when you turn professional and you have experience in moving your head in defense," she said. "You don't need to do that your first time. Maybe after you do it a couple times, take the headgear off."

Things are great for Shields, too -- she just got an $8 million fight deal with Wynn Records and Salita Promotions!!