Johnson was a first-round pick in 2005, but never lived up to expectations. His career has been marked by numerous injuries and inconsistent play.
He returned to practice last week for the first time this season after undergoing sports hernia surgery just before the start of camp. Johnson started 14 games last season and 13 in 2007.
Chargers coach Norv Turner said he envisions Johnson playing in the base package as a defensive end and in the nickel package as a tackle.
"And he does both at a real high level," Turner said. "How quickly you can get him in the mix and up to speed, that depends on the guy."
The Chargers acknowledge -- through their actions -- that their defensive line is an area of concern. They let defensive end Igor Olshansky leave as a free agent to Dallas in the offseason, and his replacement, Jacques Cesaire, had his training camp derailed with a calf injury and hasn't worked in about three weeks.
Ryon Bingham, who plays behind Cesaire, has been out with an arm injury that is considered serious. Earlier in camp, Turner declined to shoot down speculation that Bingham could end up on injured reserved, which would erase the possibility of him playing this season.
"We haven't made a decision on Ryon as far as long-term," Turner said Monday. "But (Johnson) kind of gives us another guy."
Veteran Jamal Williams, a three-time Pro Bowl tackle, and end Luis Castillo are the other starters up front -- with Cesaire, if healthy -- in the 3-4 alignment.
Turner wouldn't bite when asked if securing the 6-foot-3, 311-pound Johnson addressed a key need.
"He's a good football player and when guys become available you have to look at them," Turner said. "We are young at that position; I don't know that we are thin. But we are young at that position and he brings more experience."
NOTES: The Chargers signed their last draft pick, WR Demetrius Byrd, to a four-year contract. Byrd was selected in the seventh round out of LSU. He was injured in a car accident just prior to the April draft. Turner wouldn't specify Byrd's injuries, but it's believed Byrd won't be practicing soon. ... The team got a jump on Tuesday's roster cuts by releasing WRs Greg Carr and Rodgeriqus Smith, and T Dan Gay. All were undrafted free agents. ... The Chargers could be looking for help at cornerback. One week after cutting backup Cletis Gordon, rookie Brandon Hughes, a fifth-round draft pick, suffered what Turner called a "significant" knee injury in Saturday's exhibition loss at Atlanta. "It will be a while before he is able to go," Turner said.