Tennessee coach Derek Dooley talks with reporters during Southeastern Conference Football Media Days, Thursday, July 21, 2011, in Hoover, Ala. (AP Photo/Dave Martin)

KNOXVILLE - There's just one proven every-down player returning on the defensive line.

The linebackers, undersized or inexperienced, are essentially a mystery.

Of the many concerns University of Tennessee football coach Derek Dooley has going into the Volunteers' preseason camp that starts when players report Monday, how quickly UT can address the problems in its front seven is probably near the top of the list.

"Defense is a little bit like offense was a year ago," Dooley said at Southeastern Conference media days last week. "In this league, as we all know, if you don't have a good front seven, a productive front seven, you're going to have a tough time week in and week out."

Malik Jackson is the lone proven player back on the Vols defensive line, a group that's depending on significant contributions from junior-college transfer Maurice Couch and converted offensive lineman Daniel Hood at tackle and a handful of unproven commodities at end. Hood needed barely half a spring practice to stake his spot in the rotation, and Couch comes in with plenty of hype. Ends Jacques Smith, Willie Bohannon and Marlon Walls have played before, but now their roles are expanded.

Regardless of the who, the 6-foot-5, 270-pound Jackson, the Southern Cal transfer who flourished after a midseason switch from end to tackle last year, knows the what: he and the Vols really need a player or two to step up and provide some help.

"I need that a lot," Jackson said. "I'm trying to get these young guys to understand that I can't be the only one out there making plays, and I won't be. I'm trying to get these other guys to step up and be playmakers too so it makes it a little bit easier on me.

"If you don't have a strong defensive line, you're going to be back with the safeties on run plays, and that's not good for anybody."

Forcing its safeties to make plays might not be as bad for the Vols as some other teams, though. The tandem of Janzen Jackson and Brent Brewer - if Jackson can continue to manage the off-field issues that forced his temporary withdrawal from UT in February - has the potential to be one of the better back lines in the SEC, as well as the strength of UT's defense.

"He's on the team," Dooley said of Janzen Jackson, "but I said from the very beginning just because he's on the team doesn't mean he's back and he's good. He's still working through a lot, and we still operate with the possibility that he may not be on the team."

That's fine for Malik Jackson, who's confident in the rest of the players fighting for playing time in the Vols' now crowded secondary. UT didn't lose a single defensive back from last season, and seven new ones have arrived, including junior college transfer Byron Moore, who could start at one cornerback spot.

"Janzen's a big part of our defense, and we're glad to have him back," Malik Jackson said. "But at the same time, we've got a lot of guys who want to compete for that job and who want to play. We have a lot of young guys, and we brought in a lot of guys, so whoever wins the job wins the job. It's not set it stone. I'm ready for some competition in this thing."

The Vols' biggest question mark, however, might at the linebacker positions. Herman Lathers, who fractured his ankle during an offseason workout in early June and could be out until September, was UT's leading returning tackler and the Vols' lone returning starter at linebacker.

UT's media guide lists sophomore John Propst as a starter in the middle and seniors Austin Johnson and Daryl Vereen as starters at the two outside spots. Johnson, one of UT's biggest linebackers at 6-2 and 240 pounds, was arrested Sunday morning for public intoxication and disorderly conduct, and Dooley has not announced his punishment.

The inexperience and lack of size could mean an opportunity for A.J. Johnson, the 6-3, 245-pound freshman, to work his way into a key role. Greg King and Nigel Mitchell-Thornton could also provide depth.

The Vols have a month of camp in August to prepare for the season, but the answers to their questions on defense may take longer to find.

Said Dooley, "We're going to have to figure out ... who are going to be our players that are going to make a difference for us."