PHILADELPHIA (973espn.com) - The Eagles are probably on the clock when it comes to Jim Schwartz, their highly-regarded defensive coordinator who inherited one of the NFL's worst defenses and quickly turned into one of the best over a two-year span.

If the Super Bowl champs have another big season it's almost inconceivable that Schwartz, a former head coach in Detroit who has the personality for the big chair in any city, reaches Year 4 in South Philadelphia.

So it's paramount the Eagles take advantage of their remaining window with one of the best defensive minds in the game.

The engine of any Schwartz defense is up front where a one-gap attacking unit, which often lines up in a gasp ... wide-9 look,  is supposed to create chaos in the opposing backfield.

CHANGES TO THE DEEPEST D-LINE IN FOOTBALL

Philadelphia's defensive line was arguably the NFL's best last season and unquestionably the deepest. This year's version figures to be a little different but even better, at least on paper, as familiar names like Vinny Curry and Beau Allen, who both landed in Tampa Bay, are replaced by proven veteran Pro-Bowl selections like trade acquisition Michael Bennett and free-agent pickup Haloti Ngata.

CONCERNS

There are some concerns, however, notably the back surgery that will likely keep Tim Jernigan out of the lineup until perhaps midseason, the post-30 status of Bennett, Ngata, Brandon Graham and Chris Long.

Other worries are the heath of both Graham (ankle) and Ngata (biceps), who are recovering from surgeries, Bennett's trumped-up legal issues in Houston, and the Eagles' inability to get something done on the contract front with Graham, who is set to enter his walk year as a Super Bowl hero.

For now, Ngata, the 34-year-old run-stuffing specialist, will likely take over for Jernigan next to Fletcher Cox, perhaps Philadelphia's best player regardless of position, on the interior.

Schwartz and defensive line coach Chris Wilson will want Ngata on a pitch count, however, meaning another body inside must emerge while the Eagles wait for Jernigan to return to the lineup.

The top options for that role are all unproven: Destiny Vaeao, second-year player Elijah Qualls and Aziz Shittu, a player Doug Pederson singled out as having an excellent spring.

What makes things a little easier on that front is that Graham and Bennett are both so versatile they can each move inside in the nickel defense.

BEST POSITION GROUP IN NFL?

Defensive end is Philadelphia's deepest position and one of the top units in all of football with Graham and Bennett ably supported by Long and 2017 first-round pick Derek Barnett, a player the Eagles believe is a future star.

Meanwhile, the team loves the potential of 2018 fourth-rounder Josh Sweat as a weak-side edge rusher and the unheralded Steven Means is one of the best practice players you will ever see, a low-key reason why the Eagles' offensive line is so good and prepared on a week-to-week basis.

Also, keep an eye on undrafted free agents Bruce Hector and Joe Ostman. Hector is an interior player who got the most money to sign in this year's undrafted class while Ostman is an undersized edge rusher who was extremely productive at Central Michigan and has the non-stop motor that will drive opposing offensive linemen nuts.

DEPTH CHART:

RDE1 Michael Bennett - The best defensive lineman on the best defense of the generation. Not a bad addition but age (32) and legal issues have to be monitored.
UT1 Fletcher Cox - Team's best player whose stated goal is NFL Defensive Player of the Year.
NT1 Haloti Ngata - Aging two-down player who can still dominate as a run-stuffer.
LDE1 Brandon Graham - Maybe the NFL's most underrated star defensive lineman. Two-way player who can slide inside as a pass rusher.
LDE2 Chris Long - Fit in great as a nickel-rushing left end. Shooting for three Super Bowl rings in three years.
RDE2 Derek Barnett - Come 2019 the Eagles believe Barnett will be their top pass rusher,
RDE3 Josh Sweat - Great pass-rushing prospect with knee concerns dating back to high school.
DT3 Destiny Vaeao - Should get a bigger opportunity while Tim Jernigan is out.

ON THE BUBBLE:

DT4 Elijah Qualls - Former sixth-round pick needs to get in better shape.
DE4 Steven Means - The Eagles will find a way to keep him. MVP of the scout team.
DT5 Aziz Shittu - Undersized Stanford product has caught the head coach's eye.

PRACTICE SQUAD HOPEFULS:

DT6 Bruce Hector - South Florida product could surprise as an UDFA.
DE5 Joe Ostman - Relentless pass rusher but may be too small for NFL run support.
DT7 Winston Craig - Will have to pass a lot of names in training camp.
DE6 Danny Ezechukwu - At 6-foot-2 and 250, it's tough imagining him as a 4-3 end.

NFI LIST

DT Tim Jernigan - Suffered a herniated disc while working out but seemed to be coming along nicely in the spring. Is not expected to be ready for Week 1.

DL POSITION GRADE: 8.5

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-John McMullen covers the Eagles and the NFL for 973espn.com. You can reach him at jmcmullen44@gmail.com or on Twitter @JFMcMullen