The linebacking corps is the heart of any defense, and it's a position that struggled to make a lot of impact plays for the Detroit Lions in 2016.

No sacks, interceptions or forced fumbles from Detroit's linebackers in 2016, which is kind of hard to believe.

Tahir Whitehead finished in the Top 10 in total tackles (132), but the loss of DeAndre Levy for 10 games to a knee injury had a negative impact on the defense overall. When Levy returned at the end of the year, he wasn't the same player.

What kind of player the Lions expect him to be in 2017, after back-to-back injury-riddled seasons, will go a long way in determining how big of a need the position is in free agency and the draft.

"I think he can be the same player he was a couple years ago," Lions GM Bob Quinn said of Levy after the season.

"It looks like to me he was getting healthier and healthier as the weeks went on when he came back. That's what we envision."

Antwione Williams showed some promise as a rookie, and could continue to improve in year two.

Still, there are a lot of talented linebackers in this draft, and the Lions could be in a position at pick No. 21 to select a good one.

With the NFL Scouting Combine fast approaching, here's a look at some of the linebackers to keep an eye on during the week in Indianapolis:

REUBEN FOSTER

School: Alabama

Ht/Wt: 6-1, 228

Best trait: Speed, agility, instincts and aggressiveness. Foster checks all the boxes in what teams would want in a linebacker. He was a unanimous first-team All-American and All-SEC pick, and also won the Butkus Award as the nation's top linebacker. He led Alabama with 115 tackles (13 for loss) and also chipped in five sacks. CBSSports.com analyst Rob Rang described Foster as "a heat-seeking missile hell-bent on destruction."

Concern: The medicals at the Combine will be important for Foster. He's not taking part in drills after undergoing offseason shoulder surgery. He had a problem with frequent stingers early in his career.

The skinny: The term "sideline-to-sideline" linebacker is used too often, but it certainly fits in Foster's case. He has speed, power and cover ability that makes him a three-down player in this league, and able to play all three spots in a 4-3, though the WILL might fit his skillset best.

ZACH CUNNINGHAM

School: Vanderbilt

Ht/Wt: 6-4, 230

Best trait: He's a playmaker. Cunningham led the Commodores in tackles for loss (16.5) and forced fumbles (four) as sophomore in 2015. He followed that up by leading Vanderbilt with 125 tackles and another 16.5 for loss this past season. He has a knack for playing in opposing backfields.

Concern: He's more tall and athletic at 6-foot-4 than he is stout. At that height, he can sometimes play with a high pad level and subsequently miss tackles.

The skinny: Cunningham recorded 295 career tackles (39.5 for losses), seven forced fumbles and six sacks during three seasons with the Commodores. He recorded 19 tackles in a game in Georgia this past season. His athleticism and production should translate nicely to the NFL.

JARRAD DAVIS

School: Florida

Ht/Wt: 6-2, 238

Best trait: Davis is a great leader with impeccable character. He tried to gut through an ankle injury that eventually forced him to miss four games this past season. He had 98 tackles, 11 for loss, 3.5 sacks and four pass breakups as a junior in 2015.

Concern: He won't be taking part in any drills at the Combine because of his injury. He expects to do a full workout, including the 40-yard dash, at his Pro Day later in the spring, according to NFL.com's Ian Rapoport.

The skinny: He's a terrific athlete with great flexibility for his size. He can cover ground and knows how to finish when he gets there. He seems like a good fit as a 4-3 outside linebacker.

HAASON REDDICK

School: Temple

Ht/Wt: 6-2, 237

Best trait: He stood out at the Senior Bowl as a player with a knack for the football. Coaches down there moved him off the line of scrimmage, where he mostly played at Temple, and he didn't skip a beat. He was around the football all week. His production last year at Temple certainly sticks out. It earned him all-conference recognition as he was third in the nation with 22.5 tackles for loss. He led the Owls with 10.5 sacks.

Concern: He's a bit undersized to play as an outside 3-4 linebacker in the NFL. Teams that run a 4-3 will like that, and Reddick could fit in nicely as a WILL in a 4-3, but he'll have to continue to work on his game and expand his duties in that role.

The skinny: His speed and athleticism was on full display at the Senior Bowl, and it likely turned some heads. He has good instincts for the position, and his 22.5 tackles for loss show that he's a playmaker. He can play a lot of different roles.

TAKKARIST MCKINLEY

School: UCLA

Ht/Wt: 6-2, 265

Best trait: He has a relentless motor when you watch him. He received first-team All-Pac 12 honors as a senior after 18 tackles for loss, 10 sacks, and six pass breakups.

Concern: He looks to be more of a 3-4 pass rushing outside linebacker than 4-3 backer. The former track standout makes a lot of plays on hustle and speed rather than having a refined pass-rushing game.

The skinny: He's a super athlete, who saw a quick and drastic rise in his production as a senior. He has great speed for his size, and will be able to move around and play a few different roles in a creative defense. 

RAEKWON MCMILLAN

School: Ohio State

Ht/Wt: 6-2, 243

Best trait: Production. He recorded over 100 tackles in each of his last two seasons in Columbus. He has NFL-caliber size and strength.

Concern: He's not an explosive athlete for his size. He's your typical Big Ten MIKE linebacker. He's a little better coming downhill against the run and playing at the line of scrimmage than he is playing in space.  

The skinny: NFL.com's Lance Zierlin thinks McMillian will probably end up as a SAM in a 4-3, and can be an "average" starter in the NFL.