Daryl Smith has been a cornerstone of Jacksonville's defense for nearly a decade, playing all three linebacker spots and consistently making key plays all over the field.
He also missed just three games during his first eight years.
So sitting out the first five games this season with a groin injury has been frustrating for him and trying for his defensive teammates.
The Jaguars (1-4) rank 29th in total defense, a significant drop-off from 2011, but believe they can turn things around with Smith's expected return this week against the Oakland Raiders (1-5).
"It changes everything," fellow linebacker Russell Allen said. "He's our best player on defense. Anything that you ask a linebacker to do, he's the best we have at it. He's our best blitzer. He's our best cover linebacker. He's stout against the run. He's smart. You name it, he brings it. We get better at everything with him on the field.
"We're excited to get him back."
Smith injured his groin in training camp and missed the entire preseason. He returned to practice the week before the season opener, but suffered a setback. He hasn't practiced at full speed since.
"I know that I'm feeling pretty good," Smith said. "It's been difficult. Once it happened, I had no control over it. I'm not going to waste my time worrying about stuff I have no control over. I'm just going to do what I can to get back."
Smith might not be the only Jacksonville player to return against the Raiders.
Defensive ends George Selvie and John Chick are back at practice after sitting out the first five games because of knee injuries. Selvie was hurt in the preseason. Chick started the season on the physically unable to perform list following surgery in December.
Chick practiced in full pads Wednesday for the first time since his injury and is most likely a couple of weeks from a full return.
Selvie, meanwhile, is expected to make his season debut Sunday. He could provide a much-needed boost for a defense that has a league-low three sacks this season.
"The more the better," linebacker Paul Posluszny said. "The more healthy (guys) we have, the better, because we're able to do more things. We feel that could make a huge difference for us."
Jacksonville's lack of pass rush has been the team's No. 1 issue this season.
Jeremy Mincey, who signed a four-year contract worth $20 million in March, has five quarterback pressures. Rookie Andre Branch has been mostly a nonfactor, too. Defensive tackle Terrance Knighton has been benched in favor of C.J. Mosley. And former first-round pick Tyson Alualu hasn't been the same since offseason knee surgery.
Depth has been part of the problem, with Mincey playing nearly every snap while Selvie and Austen Lane opened the season on the sideline.
Smith should help, too.
He set a franchise record with 15 tackles for loss in 2011. He also has 1,084 tackles, 21½ sacks, 29 passes defended and nine forced fumbles.
"He's our best defensive player," Posluszny said. "It's a significant difference when he's out there and when he's not. He's a guy that can change some things on the field, so to have him back really helps our defense across the board. You just know that you've got a guy that's completely reliable and someone you can always depend on to do the right things all the time.
"He doesn't need extra help. He's a true pro. Just his presence makes an enormous difference."