... and he's not kidding.

That bad blood between the two fighters goes back to May 2019 -- when they clashed backstage at a UFC event, resulting in Masvidal socking Edwards in the face multiple times.

Or as Masvidal described it ... he hit 'em with a "3 piece and a soda."

29-year-old Edwards -- the #3 ranked UFC welterweight -- felt the attack was basically a flurry of unprovoked cheap shots ... and now he's hellbent on revenge.

"What happened with me and him, that's away from fighting. That's street stuff," Edwards tells TMZ Sports.

"So, if that's what he's about, we’ll do it that way."

Of course, Edwards would rather get PAID to fight Masvidal -- so, he's hoping the UFC puts that bout together. But, if not, they're still gonna scrap.

"You best get your ass in the Octagon 'cause it's either on the street or in the Octagon but you're gonna get it."

"Wherever you want it, you choose, in the Octagon or on the street, I'm good to go either way."

But, before that fight happens, Edwards -- who's on an 8-fight win streak -- is set to take on Belal Muhammad at UFC Fight Night 187 on Saturday.

Edwards is confident he'll run through Muhammad -- setting himself up for a shot at the welterweight title

What's interesting ... Edwards hasn't lost a fight since 2015 -- and the last man to beat him is the reigning welterweight champ Kamaru Usman.

We also talked to Edwards about Khamzat Chimaev -- who Leon was supposed to fight on multiple occasions.

But Khamzat -- one of the most exciting young fighters in the UFC -- has been battling COVID and there's a timetable set for his return.

"As far as Khamzat, I kinda put him behind me because he's only had 2 fights, 3 fights in UFC," Leon says.

"He got little health issues now so I wish him well, wish him full recovery, that's number one. If he works his way up the division then for sure, I intend to fight him."