TMZ Sports spoke to the 34-year-old UFC star ahead of his scrap with Dustin Poirier on July 29 ... and the Baddest Mother F****r belt is on the line. We asked Gaethje if he cared about the strap.

"I think [the belt is] really iconic," Justin said.

"There's only been two guys in the world that have ever fought for it. We'll be the two out of four guys now. And I think it's, it does great things for the legacy, that's ultimately what we're here to build is a legacy. Make money. That's there. And, you know, it catapults us right into the championship talk. So it's perfect."

FYI, only Nate Diaz and Jorge Masvidal have fought for the belt ... which was created for them. Gamebred won that November 2019 fight by TKO ... and that's the last time the belt was on the line.

It'll be a rematch for Dustin and Justin ... the guys fought in a Fight Night card in April 2018. DP beat JG by 4th round TKO. It was just Gaethje's third UFC fight.

"It's part of my journey. It's something that I'll cherish forever, but you know, I don't think it's a huge factor," Gaethje said of the first fight's impact on UFC 291, adding ... "It's five years ago."

"We both grown so much and we've both been in some huge fights since that day. So yeah, I think it's again something that I'll always cherish, but it's not something that I'm using to game plan for this fight."

We also Justin where he believes a win would leave him in his quest for the 155-pound title.

"I'm not too worried about that right now. [Dustin's] the number two-ranked guy in the world. I'm the number three-ranked guy in the world. I think no matter what it's a given that the winner of this fight, we either fight the winner of the [Islam Makhachev-Charles Oliveira]. And if one of us is able to go in there and get a quick knockout and take no damage, then there's a slight possibility that maybe we'll be ready for October."

Makhachev and Oliveira are fighting at UFC 294 on October 21 in Abu Dhabi.