A tough week for the Jaguars' defense got even tougher Friday.
Derek Cox, a third-year veteran starting cornerback, was placed on the season-ending injured reserve list by the Jaguars Friday, the same day starting defensive tackle Terrance Knighton expressed uncertainty over whether he will play again this season.
The Jaguars earlier this week placed starting linebacker Clint Session on IR with a concussion, and last week they placed starting cornerback Rashean Mathis (knee) on the season-ending list.
Starting defensive end Matt Roth and Knighton also are out Sunday, meaning five starters will be out of the lineup against one of the NFL's best offenses Sunday.
"We always preach it can happen quickly," Jaguars Head Coach Jack Del Rio said Friday 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.
"You need to be preparing in a way that you are developing as a player and that you are in a position to help this football team at some point. If you're not approaching it that way, we're going to find somebody else. With some of the guys who are going to play, we'll find out how well we've done in developing some of these guys and how much attention they've been paying.
"You hate to have this many guys, but that's the way we approach it."
The Jaguars signed quarterback Dan LeFevour off the Colts' practice squad to take Cox's place on the roster. Under NFL rules, LeFevour must be on the Jaguars' active roster at least three games.
LeFevour (6-feet-3, 230 pounds), a sixth-round selection in the 2010 NFL Draft by Chicago, spent last season on Cincinnati's 53-man roster. He was waived by the Bengals during the final cuts this season and signed to the Colts' practice squad November 9.
The Jaguars now have an NFL-high 17 players on injured reserve this season.
Cox, who had 10 passes defensed this season, sustained the injury in a loss to Cleveland Sunday. He practiced limited Wednesday, but Del Rio said when swelling in the knee did not subside subsequent tests revealed damage that necessitated the move to IR.
"The swelling persisted, so we wanted to make sure we took a look," Del Rio said. "It wasn't anything you could feel with the exam. The MRI revealed a problem."
With Cox and Mathis each out for the season, six-year veteran Ashton Youboty and third-year veteran Will Middleton will start at corner, with Drew Coleman continuing as the nickel back.
"We've had solid play from the majority of our defense throughout the year," Del Rio said. "Derek and Rashean – those guys had been doing well, and that has been expressed in how the whole defense had been playing."
Youboty played about 20 plays last week against Cleveland, and Del Rio on Friday was asked how ready Youboty is for a more extended role.
"We're getting ready to find out," Del Rio said. "He played last week and was going to play more this week. Clearly, we're going to be counting on him."
Youboty and Middleton aren't the only backups now in starting roles for the NFL's third-ranked defense. C.J. Mosley will start a third consecutive game for Knighton at defensive tackle, and Leger Douzable is expected to start for Roth. Russell Allen will start at outside backer for Session.
"The 11 we had going at full strength was a good 11, very capable," Del Rio said. "Now, it's incumbent on guys who are getting the opportunity to step up, fill in and fight for us and scrap. We expect to continue to play good defense."
Knighton, who started the first eight games of the season, has missed the last two games with an ankle injury. He said Friday he is waiting to hear from specialists before deciding if he will play again this season.
Knighton previously never had missed a game in three NFL seasons.
"I'm just waiting to hear back from doctors to see what's going on and taking every precaution I can," Knighton said. "It feels fine. I'm just waiting for the doctors, to see what they think. I still want to play. I feel fine. I can run on it, but certain cuts, they're worried about. They don't want me doing that. I'm still progressing and I haven't lost hope for the season.
"In the meantime, I'm here working out and making sure I keep conditioning."
Del Rio said the Jaguars remain hopeful Knighton will play again this season.
"We'll see how it goes," Del Rio said. "We're doing all we can to continue to keep him in condition, to rehab him and keep him involved in meetings. We remain hopeful."
*Cox (knee), Knighton (ankle) and Roth (concussion) did not practice, with defensive end Aaron Kampman (hamstring) working limited for a third consecutive day. Kampman is listed as questionable and has not played in the last two games. While Douzable is expected to start for Roth, George Selvie and John Chick also will play extensive roles.
*Fullback Brock Bolen (calf), Chick (abdomen), wide receiver Brian Robiskie (hamstring), wide receiver Cecil Shorts (hamstring) and offensive tackle Guy Whimper (thigh) practiced full and are listed as probable for Sunday.