Kampman, considered the team's top free-agent signee this offseason and a player who had become a team leader in less than a year with the team, sustained a torn right anterior cruciate ligament in practice on Thursday, the team announced early Friday afternoon.
According to Tania Ganguli of the Florida Times-Union, the injury occurred in a non-contact pass-rush drill.
Kampman, who called Thursday's incident a freak occurrence, missed the last seven games of last season with the Green Bay Packers with a torn ACL in his other knee.
He told reporters Friday rehabilitating and returning last season made him a better person.
"It's not a feeling you want or ever want to feel again," Kampman said. "There are definitely more lessons to learn."
Kampman -- as he did with last season's ACL tear -- will opt to have patella replacement surgery, according to multiple reports.
"You never look back," Kampman said. "You always look forward."
Kampman, who had 54 sacks in eight seasons with Green Bay, had registered four sacks in eight games this season with Jacksonville. Teammates had talked all season of the leadership Kampan had brought on and off the field, and his absence will be a major loss for a team still fighting for a playoff spot.
"This goes out to a great man of god, father, husband and teammate," Jaguars quarterback David Garrard tweeted moments after the team received the news around 12:30 Friday. "Aaron Kampman we love you and we'll miss your presence."
Jeremy Mincey, who moved past former first-round selection Derrick Harvey into a starting defensive end job, is expected to return Sunday after missing the Jaguars' last game with a fractured hand. He and Harvey likely will start Sunday, Ganguli reported.