TMZ Sports talked to the 31-year-old, #1 light heavyweight contender ... and we asked Jiri if Alex presented the biggest challenge to him over his 10+ year pro-MMA career.

"I will see that when I face him. I will feel that who is he. But what I've saw with his style, I think I've fought with more dangerous guys."

Surprising ... until you look at the opponents he's shared an Octagon with over the years, including Glover Teixeira (submission win, 2022), Volkan Oezdemir (KO win, 2020), and Dominick Reyes (KO win, 2021).

But, as good as those fighters are, none possess the crushing knockout power of Poatan (8-2, 6 KO) ... especially when it comes to his vicious left hook. Alex has put many men to sleep with that shot over the years.

We asked Jiri, a dynamic striker in his own right, if he believed he could win a stand-up battle against Alex, assuming things don't go to the ground where Prochazka would seemingly have the advantage.

"Yes, yes. 100 percent yes," Prochazka said without any hesitation.

Of course, the guys are fighting for the belt held by Jamahal Hill ... who ruptured his Achilles a few months ago.

We asked Jiri what it'd mean to him to once again have the UFC championship belt wrapped around his waist ... and he was at a loss for words.

"I can't talk about it. You will see that in Madison Square Garden, and I believe in that."

As for Pereira, we talked to him, too ... and let's say he sees things going a bit differently.