The Weigh-In: UFC 189, Aldo's injury, more

Each week, our ESPN.com panel tackles hot topics in the world of mixed martial arts.

This week, UFC lightweight Dustin Poirier joins our expert panel.

1. UFC 189: Chad Mendes vs. Conor McGregor. Who wins, how and why?

Dustin Poirier: Chad by decision. I would pick Conor over Jose Aldo, but Chad over Conor. Styles make fights. I think it's a bad matchup for Conor. [It's] striking a little bit -- I could see Chad landing a big overhand; he has good power and Conor does get hit -- but it's more the wrestling. He's going to control the fight.

Brett Okamoto: McGregor by knockout in the third round. If Mendes wins I think it will be early and I actually think it will be a punch that does it, not his wrestling. Everyone is obsessed with the "McGregor vs. a wrestler" question, and I get why, but asking Mendes to dominate a 25-minute fight on the ground, when he had no training camp, is asking a lot. I see Mendes having a great first round, because he's a great fighter, but when signs of fatigue start to show up in the second and third rounds, McGregor will take advantage and put the fight away.

Michael Huang: My feeling is if Mendes can push Jose Aldo to the limit, he'll be able to do the same to McGregor. I don't think we can underestimate Mendes' wrestling and what he'll be able to do if he can get McGregor to the ground. I've not seen McGregor really tested there, simply because he's so good at staying on his feet. Now, that being said, Mendes' stand-up game, while very much improved, is less than McGregor. If he can stay out of harm's way, change levels and his gas tank is as good as he says it is despite the short notice, it's Mendes in three.

2. UFC 189: Robbie Lawler vs. Rory MacDonald. Who wins, how and why?

Poirier: Robbie by finish. He has been looking like a killer in the gym. He's way better than the first time they fought [in November 2013]. I know Rory is as well, but Robbie is the champ for a reason. He's just too aggressive, always trying to hurt you from every angle. Shutting him down is a tough thing, especially for five rounds. That first fight, it looked like it was starting to shift in Robbie's favor the longer it went. Now add two rounds to that. He's going to finish Rory. [Note: Poirier is a teammate of Lawler at American Top Team.]

Okamoto: I'm already on record picking MacDonald by decision, but the closer the fight gets, the more I'm wanting to switch to Lawler. Fate, if you believe in such a thing, seems to be on MacDonald's side. Considered a phenom for so long, the heir to Georges St-Pierre's throne, now 25, in his first title fight -- it just feels like MacDonald should put it all together here. His wrestling could be an X factor. In a close, championship fight, it's not a bad idea to pick the fighter with better wrestling, who is more conscious of winning rounds. MacDonald will be playing chess out there, while Lawler looks for a fistfight. I'll stick with my MacDonald pick, but it's not a confident one.

Huang: I'll take Lawler here by TKO in the fifth. I look at how Robbie approached his two fights with Johny Hendricks and see that in their first fight, he ran out of gas after getting taken down repeatedly in the fifth. In their second fight, Lawler looked gassed in the fourth but had a fifth-round spurt to basically win him the title. I think McDonald is entirely hittable. Lawler's not the most accurate, but he could get a tired McDonald with one of those spurts. I am still not sold on MacDonald. Never have been. Lawler's got him once already, I think it's a second win here, too.

3. UFC TUF Finale: Jake Ellenberger vs. Stephen Thompson. Who wins, how and why?

Poirier: Ellenberger by decision. Thompson is a good striker but I don't think he really has the power to put Ellenberger down. Ellenberger is more of a grinder and I think his wrestling is an advantage. I know Matt Brown is a great fighter, but didn't Matt Brown beat Thompson by wrestling him a little? If Matt Brown can out-wrestle you, I think Ellenberger can. And that's not a knock on Brown, Ellenberger is just a good wrestler.

Okamoto: I'll also go Ellenberger, but by TKO. Thompson is a lot of fun to watch but I think pressure and the dual threat of power punches and effective takedowns will be his kryptonite. Ellenberger hasn't looked like a confident welterweight as of late, losing three of his last four, but that was against absolutely stellar competition in Robbie Lawler, Rory MacDonald and Kelvin Gastelum. Even though he's coming off a win over Josh Koscheck, his back is still pretty much against the wall here and I think he'll respond to that.

Huang: Ellenberger needs a win badly but I don't think it'll be against "Wonderboy." I'll take "Wonderboy" by decision. His takedown defense is very much improved and he's got the length to keep Ellenberger's wrestling at bay. The key will be the jab -- stay accurate and stick and move. I don't think you'll see Thompson go with a lot of kicks, just because he should keep his feet mobile and not offer them up for Ellenberger to catch. In the end Thompson doesn't have to knock out Ellenberger, but he could point him to death and really make hamburger of his face.

4. UFC Fight Night: Frank Mir vs. Todd Duffee. Who wins, how and why?

Poirier: You need to bet on all these picks I'm saying, because these are all going to happen. Duffee is going to knock Mir out. It's not going past two. Mir's on the downslope for sure, but Todd is just an incredible athlete. He's a big puncher, fast, he's in great shape and ready to go. I think he's going to finish him in the first round. He saw a big opportunity in a fight he knew he could win and good for him, because he is going to win it. [Note: Poirier is a teammate of Duffee at American Top Team.]

Okamoto: Duffee by KO. Other than the fact this is a heavyweight fight and crazy things tend to happen in heavyweight fights, Duffee has no business losing this fight. Mir is one of the greatest UFC heavyweights of all time, but wear and tear has slowed him down substantially and he has never been a dominant wrestler. Duffee should be able to control where this fight goes and make the most of his obvious physical advantages in this matchup. As long as he doesn't get in his own head and struggle to pull the trigger, I see Duffee putting this one away inside five minutes.

Huang: I'm with Okamoto on this one. I'm going to take Duffee by KO, too. There's no pressure on a guy who's coming back after going through some of the personal issues he has had. And he's fighting a guy in Mir (albeit a former champ) who has lost four in a row. No pressure -- Duffee will be loose and confident. He just can't leave an arm or leg open for a crafty jiu-jitsu expert like Mir.

5. In memory of the Aldo-McGregor fight, should a UFC champion be defending spinning back kicks in training, less than three weeks out from a title fight?

Poirier: I've heard so much stuff, that his ribs are broken, they're strained, they're fractured. I heard he was cleared to fight and still backed out. If he did get hurt in training, which I'm sure he is injured, that's just part of the sport. You're fighting a guy with spinning back-kicks -- you need to see them. You can't be seeing them for the first time in the fight. What was it, 2.5 weeks out from the fight? Yeah, that's still your hard sparring time. I'd tell my sparring partners to stop throwing that with a week left. I've never heard of any kind of cover you could wear to protect against that. They make compression shirts with a gel or something on the side, but how much is that really going to help against a heel? You just need training partners that aren't trying to hurt you, that are just trying to make you better.

Okamoto: Yes. As easy as it is to throw blame at Aldo for the injury, it's irresponsible. As Poirier said, he has to train for the spinning back kick. He has to prepare himself for unorthodox striking. It would be one thing if he were training with a complete novice, who just signed his gym membership that day, but the lightweight who kicked Aldo in the ribs is a professional fighter, who has been with Nova Uniao for years. Aldo has pulled out of his share of fights, and each time it's been disappointing, but he's also won every fight he has ever had in the UFC. Training hard leads to injuries, but it also leads to wins. Chalk this up to bad luck, for all of us (besides Chad Mendes).

Huang: That's on his coaches, man. C'mon, they should be smarter than that. I know they are training for a title fight, and practice should always be tougher than the real thing. And indeed, he has to be prepared for that technique. But perhaps the frequency or intensity of those spinning back kicks could have been gauged.