Joaquin Buckley Says Kamaru Usman Is Toughest Fight Of His Career

Kamaru Usman has lost three fights in a row ... but Joaquin Buckley, the man fighting the former champ Saturday night in the main event of UFC Fight Night, tells TMZ Sports that doesn't even begin to tell the full story!

In fact, not only does Buckley NOT believe Usman's washed ... he actually feels that on paper, this is the toughest test of his career -- and that's coming from a guy who has fought and defeated Colby Covington, Stephen "Wonderboy" Thompson, and Vicente Luque!

We spoke with 31-year-old Joaquin -- the number 7th-ranked UFC welterweight -- ahead of his scrap with Usman.

"On paper, it's the toughest fight that I've had. But I truly believe that all the homework that we've done in this fight, man, we're going to ace it," Buckley told us.

As for the fans who say Kamaru's done, that's not the way Joaquin sees it at all.

"[Usman] definitely could be still a champion. The losses that he had, I mean, it's still like something that you got to look at. Did he really lose? Like when he lost the first fight, he got knocked out, but he was winning that whole time. And then with the Leon, Leon got blessed by the judges to keep the belt," Buckley said of Usman-Edwards 2.

He continued ... "My man moved up to middleweight and really showed what he had on 10 days notice [against Khamzat Chimaev.] So y'all got to imagine, you're talking about a person that took two years off just for preparation to come back. So I know he's more than ready."

Buckley says if when he beats Usman, that should propel him to the number one contender slot.

"I believe we're coming for that number one spot, for real. There's nobody in the division that has done what Kamaru Usman has done. And once I do what I do to Kamaru Usman, right, and really kind of highlight that I'm the best welterweight fighter in the division, they got to put me as number one. Period."

There's a lot more with JB ... including whether he's done with the Middleweight division (he's not), so check out the full interview!

We also caught up with Usman earlier this week as well ... and he said he still believes he's the best welterweight in the promotion.