Russell Allen didn't want it this way.

But the nature of the NFL is that one player's injury often is another's opportunity, and the nature of the NFL is that backups must perform.  In that sense, Allen said he must look at the season-ending concussion sustained by Clint Session Sunday as an opportunity.

And he said he absolutely must perform.

"This is never how you want it to happen," Allen said Wednesday as the Jaguars (3-7) prepared to play the AFC South-leading Houston Texans (7-3) at EverBank Field in downtown Jacksonville Sunday at 1 p.m.

"Clint's not only a teammate; he's a friend. He's a good football player who has made a lot of plays for us, and you don't wish that on anybody, so that's first and foremost.

"But this is an opportunity to help the team. That's why I'm here, so I'm excited about it."

Session, who signed with the Jaguars as an unrestricted free agent from the Colts during training camp, sustained his second concussion of the season Sunday against Cleveland. The Jaguars placed Session on injured reserve Tuesday and signed 10-year veteran Kevin Bentley to take his place on the roster.

Jaguars Head Coach Jack Del Rio said Wednesday Allen will start in Session's place against Houston.

"I'm confident he knows what he's doing and I'm confident he'll give us everything he has," Del Rio said. "Russell's a good, solid backup linebacker for us and he plays a solid role on special teams. We're going to ask him to increase his responsibility and play as a starter now – and continue to do some things on special teams for us.

"I trust in the work he's putting in getting ready to play a little bit bigger role for us."

Allen, who signed with the Jaguars as a rookie free agent in 2009, said while he has played more outside backer than middle in three seasons, he is comfortable at all three spots.

 "I take equal reps everywhere," Allen said. "That's something I take a lot of pride in, is to be able to play all three positions effectively in case something were to happen."

The injury to Session is yet another blow to the Jaguars' third-ranked defense. Not only has defensive end Aaron Kampman missed six games, the team also has been without defensive tackle Terrance Knighton (ankle) the last two weeks and without defensive end Matt Roth (concussion) late in Sunday's game.

The Jaguars also have placed two starters – Session and cornerback Rashean Mathis (knee) – on injured reserve in the last two weeks.

"Any time you lose a starter, it hurts," Jaguars middle linebacker Paul Posluszny said. "It's a tough situation. You never want a guy like that to go on IR, but at the same time we're confident in the guys we have. Russell's going to step in and do a great job for us.

"It's that time of the year in the NFL. Across the board, it would be tough to find a team that is completely healthy at this point. We're no different. Guys are going to get hurt. That's part of the deal. We have a lot of confidence in the guys we have who can step in and play right away."

Also around the Jaguars Thursday:

*Del Rio said he doesn't expect the Texans to change dramatically offensively after placing quarterback Matt Schaub on injured reserve. But because backup-turned-starter Matt Leinart is left-handed as opposed to the right-handed Schaub, Del Rio said he expects the Texans to flip some of their formations and pass plays. "They're not going to scrap what they've been doing and change a whole lot," Del Rio said. "They'll tailor some things to allow him to roll (out) his way – our right, their left."

*Del Rio on playing with pride despite a 3-7 record through 10 games: "Who you are as a man and what you stand for should not waver whether things are going good or bad. You have to be who you are and stand for what you believe in. We're in a little bit of a tough situation, but you want to stay true to who you are and continue to fight. There's professional pride involved." Del Rio also said representing the Jaguars "needs to mean something. I know it means a great deal to me. I'm going to give my best each and every day. That's what I expect from our guys."

*Del Rio said he doesn't expect any particular chippiness or extracurriculars Sunday between the Jaguars and Texans. There was talk of ill feelings between the teams following Houston's 24-14 victory over the Jaguars in Houston last month, with Texans left tackle Duane Brown being fined for punching Session on the sideline following a play. Brown said afterward he lost his balance and that the incident was misinterpreted. "I think that was a little overdone," Del Rio said. "They played good football. They played to the whistle. Other than there being a balance issue over on the sideline with the one guy there was really nothing else out of the ordinary."

*Del Rio said while the Jaguars have placed a league-high 16 players on injured reserve this season, "There's no real common denominator. It's not a certain type of injury. It's just unfortunate. There are some good players who are no longer available to us right now. My motto on that is, next guy up and let's roll. That's what we have to do."

*Knighton (ankle) and Roth (concussion) missed practice. Knighton has missed the last two games, but unlike previous weeks he did not attend practice on Wednesday. Roth sustained the concussion Sunday against Cleveland. "We're going to have to wait and see on Matt," Del Rio said. "We don't know yet. Terrance also didn't practice today. We'll have to see how the dust settles at the end of the week. I can't really provide clarity."

*Defensive tackle Tyson Alualu, running back Maurice Jones-Drew and fullback Greg Jones were limited in practice for non-injury reasons to rest. That has been the case with the three players throughout the season.

*Cornerback Derek Cox (knee), Kampman (hamstring), wide receiver Brian Robiskie (hamstring) and right tackle Guy Whimper (thigh) were limited Wednesday. Kampman and Robiskie missed Sunday's game while Cox and Whimper started. Del Rio said Thursday will be a defining day for Kampman.

*Fullback Brock Bolen (calf), defensive end John Chick (abdomen) and wide receiver Cecil Shorts (hamstring) practiced full Wednesday.