ROSEMONT, Ill. – After more than two years on the sidelines, Frank Mir knows he may have to deal with some nerves before he returns Saturday night.

Mir (18-11 MMA, 0-0 BMMA) will make his promotional debut in the Bellator 198 main event against Fedor Emelianenko (36-5 MMA, 0-1 BMMA). It will be a long-discussed meeting between a former PRIDE champion in Emelianenko and a former UFC champ in Mir.

Bellator 198 takes place at Allstate Arena in Rosemont, Ill., near Chicago. The main card airs on Paramount following prelims on MMAjunkie. Their fight is part of the opening round of Bellator’s heavyweight grand prix. The winner will move on to a semifinal matchup against Chael Sonnen for the right to fight for Bellator’s vacant heavyweight title.

“I’m just trying to get back into the rhythm of what it’s like to be during a fight week,” Mir said. “I’m sure nerves are going to kick in eventually, and I’m waiting for that and a lot of other distractions leading up to it will help.”

Mir said it’s not so much nerves about fighting again after such a long layoff – a layoff even longer than when he wrecked his motorcycle in 2004 after he was UFC champ and had to vacate the title while he recovered.

And it’s not so much nerves about fighting a fellow legend like Fedor, or trying to impress his new Bellator bosses. Instead, it has a little to do with getting old.

“This is the thing all fighters my age are going to have to deal with: One bad performance …,” Mir today told MMAjunkie. “I can go smash Fedor. I can smash Chael and look like the best version I’ve ever presented. And let’s say I fight (Matt) Mitrione in the finals, (or Ryan) Bader, (Muhammed) ‘King Mo’ (Lawal). Whoever. And I go out there and have a bad performance. The very first conversation when I walk out of that cage will be, ‘Are you going to retire?’

“They were talking about retirement when I was 28. I can’t imagine when I’m 38 what they’re going to say. That’s the part that (I’ve) been apprehensive (about). Another fighter can have an off night, but if you’re an older fighter and you have an off night, all of a sudden the fat lady’s standing up getting ready to belt one out for you: ‘You should retire.’”

No matter what the outcome though, at least Mir can one day close down his career knowing he stepped in the cage with Fedor in a fight fans started talking about in the mid-2000s, and one that picked up some steam when the UFC was in contract talks with Fedor in the late-2000s.

“Of course I’ve always wanted to match up against him, and I feel like I match up well against him,” Mir said. “Fedor’s not a big guy. He’s quick and he’s fast, but that’s why I came in shape. When I’m in shape, I’m just as quick as he is. … I think it’s an interesting fight, and I’ve wanted to put myself out there and dance with him for a long time.”

Mir said he believes it’s fair to regard Fedor as one of the best heavyweights in history as long as there’s an asterisk of sorts attached to it.

That said, he won’t necessarily be prepared to be any less happy with a win over him Saturday night.

“When you talk about Fedor and you say he’s one of the best heavyweights in the world, I say, ‘Are we talking about inside a cage, or inside a boxing ring?’” Mir said. “It makes a difference, just as much as clay vs. grass if you play tennis. … In a boxing ring, PRIDE rules, Fedor is Hall of Fame, one of the top five heavyweights of all time. In a cage, he’s small, he doesn’t have good cage technique, and I don’t know if I can put him in the top five.”

For more from Mir, check out the full video interview above.

And for more on Bellator 198, check out the MMA Rumors section of the site.