Third in a series

The Raiders have a cornerstone edge player in Khalil Mack and the kind of beef coach Jack Del Rio and general manager Reggie McKenzie love on the interior with Dan Williams and Justin “Jelly” Ellis.

But the unanswered question remains second-year defensive end Mario Edwards Jr., who sustained a neck injury early in the 14th game of the season against Green Bay and finished on injured reserve.

The Raiders, particularly Del Rio, have been tight-lipped about Edwards’ status, saying they are still gathering information.

The only light was shed by McKenzie during a Super Bowl event, when he said the condition might possibly be genetic _ something Edwards has carried around with him since he was a youth.

If the Raiders are unsure about Edwards availability for 2016 and beyond, a big expenditure in free agency or a premium draft pick would be fully justified. If the news is good and they’re keeping it to themselves, the needs up front aren’t as pressing.

Regardless, the Raiders will probably be more active on the outside, with a second pass rusher, than with space-eaters. Williams and Ellis fill those roles, giving Del Rio the kind of interior he had in Jacksonville with Marcus Stroud and John Henderson, and when he was a linebackers coach in Baltimore when the Ravens had Tony Siragusa and Sam Adams.

A look at some possibilities when free agency begins March 9, as well as players under contracts and their own free agents:

UNRESTRICTED FREE AGENTS

Ends/edge players

Malik Jackson, Denver: A 3-4 end, but can he be a 4-3 tackle? Doesn’t matter. McKenzie believes in “football players,” which can fit any scheme. The exclusive franchise tag to Von Miller may leave Denver out of the running and the 26-year-old Jackson should get a huge contract in the opening days of free agency.

Olivier Vernon, Miami: Given a transition tag by Miami, the Raiders or any other team with cap space can come up with enough up-front money to get the 25-year-old pass rusher aboard. The deal Miami made with Ndamukong Suh last year eats up $28.6 million in cap space. If Cameron Wake comes free in an attempt to keep Vernon, the Raiders could look in that direction.

Chris Long, Los Angeles: One of the top ends from 2011-13 with 30 sacks and ability to defend the run, the question is whether Long at age 30 can return to that form after playing 18 games in the last two seasons. The legacy factor of bringing in the son of Hall of Fame Raiders defensive lineman Howie Long doesn’t hurt.

Charles Johnson, Carolina: With a cap number of nearly $15 million and only one sack in 2015 (he missed seven games with a hamstring injury), release was a foregone conclusion. But Johnson is 29 and still could have some solid years left. He played well for the Panthers in the Super Bowl. Would be a Justin Tuck-type acquisition for a respected veteran.

Mario Williams, Buffalo: Williams, a former No. 1 overall pick, didn’t do himself any favors by complaining about scheme and making 19 tackles with five sacks in 15 games, essentially forcing his own release. Williams’ effort level was questioned, a red flag for McKenzie and Del Rio. Williams, 31, is presently visiting Miami.

Robert Ayers, N.Y. Giants: Ayers, 30, had 9.5 sacks for New York last year. According to profootballfocus.com, he was their best defensive player and had multiple pressures in every game he played. His 48 pressures led the team.

Jason Pierre-Paul, N.Y. Giants: Pierre-Paul, 27, had no training camp and his play was limited after a fireworks accident damaged his right hand, losing his index finger and the tip of his thumb. He finished with six sacks and 34 pressures, getting better as the season went along.

William Hayes, Los Angeles: On one hand, Hayes is 30 years old, but on the other, he’s an ascending player. Played better for the Rams than in earlier stop with the Tennessee Titans and had 40 pressures and 5.5 sacks in a part-time role. In four seasons with the Rams, Hayes had 21.5 of his 29.5 career sacks despite not playing full time.

Tackles

Jaye Howard, Kansas City: In his first season as a starter, Howard, 27, was an excellent run-stuffer and also had 5.5 sacks as a 3-4 end who would likely play inside in a 4-3. He was also a beast against the Raiders, and McKenzie and Del Rio surely took notice.

Brandon Mebane, Seattle: Primarly a nose for Seattle, the general consensus is that the former Cal star has slipped some at age 31. The question is whether Mebane could thrive with fewer snaps in a rotational basis with the tackles already on the roster. Has familiarity with defensive coordinator Ken Norton Jr.

Nick Fairley, Los Angeles: Signed a one-year, $5 million contract to play with the Rams after four seasons with Detroit where the former first-round pick (No. 13 overall) never reached his full potential. Has quickness to be a nice counterpoint to Raiders size and power inside.

Paul Soliai, Atlanta : Was highly thought of by the Raiders as a member of the Miami Dolphins, but at 32 appears to be on the downside.

Haloti Ngata, Detroit: Ngata is now 32, probably still sees himself as a premiere inside player, but the Raiders’ interior strength could have them looking elsewhere.

Terrence Knighton, Washington: Rumor-mill had Knighton, 29, targeted for Raiders last season because he had played for Del Rio in Denver. Raiders instead went straight for Williams after Suh signed with Miami.

PLAYERS UNDER CONTRACT

DE Khalil Mack: Two years in, and Mack is an All-Pro at two positions, a Pro Bowler and one of the NFL’s premiere players against both the run and pass. A foundational player whose contract expires after the 2017 season _ just like Derek Carr.

DT Dan Williams: More than consolation prize when Suh signed with the Dolphins, Williams is deceptively quick and was difficult to move on the interior.

DE Mario Edwards Jr.: A second-round draft pick who looked explosive and strong enough to be a first-round pick _ until a neck injury ended his season. Still no word on its severity.

DT Justin Ellis: A training camp treat is seeing this 331-pound tackle up close during drills and scrimmage situations. Expected to take a major leap this year and agile enough to do it.

DT Stacy McGee: In his third year, McGee rebuilt his game under the new coaching staff. Had an impressive rookie year before falling out of favor in Year 2.

DT Leon Orr: Undrafted free agent was called up from practice squad. A locker room live wire and raw talent with the kind of size the Raiders love.

UNRESTRICTED FREE AGENTS

None

RESTRICTED FREE AGENTS

DE Benson Mayowa: Strong enough to hold the edge and athletic in open space, Mayowa will likely be retained.

EXCLUSIVE RIGHTS FREE AGENTS

DE Denico Autry: One of the real pleasant surprises of the 2015 season, Autry played in 14 games with eight starts, had three sacks, a safety and will be counted upon for more this season. Potentially a major find, signed as an undrafted free agent in 2014.

DE Shelby Harris: Has displayed pass rushing ability and potential in going between practice squad and 53-man roster.