JACKSONVILLE, Fla. -- Aaron Kampman brought leadership, tenacity, production and a strong work ethic to Jacksonville's defense this season.

The Jaguars are about to find out if those qualities rubbed off on his young teammates.

Kampman tore the anterior cruciate ligament in his right knee during practice Thursday, leaving the Jaguars without their best pass rusher and their defensive leader.

Kampman injured his knee during a non-contact drill. Tests Friday revealed the severity of the injury. He will be placed on injured reserve and have surgery at a later date.

"It's a shame because he's a special young man in a lot of different ways, not only on the field but in the locker room, in the community," coach Jack Del Rio said.

The Jaguars (4-4) signed Kampman to a four-year, $25 million contract in March to upgrade a defense that had a league-worst 14 sacks in 2009.

Jacksonville felt like it was getting a bargain even though Kampman tore the ACL in his left knee last November. He recovered in time to make an immediate impact this season and leads the team with four sacks and 30 quarterback pressures.

"Any time you have one of your main guys out for the year, especially with a guy that's not just a starter but an impact player, it hurts," cornerback Rashean Mathis said. "It hurts a lot. But those things happen all the time in the league, week-in and week-out it's bound to happen."