The Dallas Cowboys will be usher in the Leighton Vander Esch era this week, as Sean Lee's pesky hamstring injury will reportedly force him to miss the next two to four weeks.

Despite knowing that he wouldn't immediately start, the Cowboys decided to select Vander Esch with the 19th overall pick in the 2018 NFL Draft with Lee's injury history in mind.

Vander Esch was not only drafted to be Lee's successor but also to make sure the Cowboys defense could remain effective even when Lee is injured.

Recent history suggests that the Cowboys defense tends to take a nose dive when Sean Lee is out:

Using @TheQuantEdge's injury tool, here's how the #Cowboys fared with and without Sean Lee in the lineup last season. pic.twitter.com/Bs5XeIA6Ow — John Owning (@JohnOwning) August 9, 2018

Lee's impact on the defense goes beyond his individual contributions. Lee is one of the smartest linebackers in the NFL. He routinely puts the defense in a position to succeed on top of being one the most instinctual linebackers in the NFL.

There may only be a handful of linebackers on the planet who could step in and replace Lee without the defense missing a beat.

Asking a rookie to step into Lee's shoes is a tall task, but from what he's shown through Week 3, Vander Esch is up for the challenge.

In the first three games, the Cowboys rotated their linebackers frequently in an attempt to keep Lee healthy -- so much for that -- while getting Vander Esch experience in regular season game action. After playing 22 snaps against Carolina, Vander Esch saw much more action in Weeks 2-3 (41 against the New York Giants and 47 against the Seattle Seahawks) as Lee dealt with separate hamstring issues.

While he performed well in his given opportunities in Weeks 1 and 2, his performance against the Seahawks was his true coming out party.

While he wasn't tested in the pass game, Vander Esch impressed against the run. He finished the game second on the team in tackles (six), per Pro Football Focus, displaying quick mental processing, impressive athleticism and an improved ability to play off blocks.

Even though the Cowboys are in their nickel defense (four defensive linemen, two linebackers, five defensive backs) with safety Jeff Heath in the box, Vander Esch is essentially lined up as the "Mike," or middle, linebacker spot.

After the ball is snapped, Vander Esch mirrors the steps on the running back, which allows him to effectively flow play side as he reads the blocking scheme up front. Notice how Vander Esch stays square to the line of scrimmage as he is mirroring the running back's steps, this would allow Vander Esch to change direction quickly if the running back cuts back.

Once Vander Esch reads the running back bouncing the ball outside, he turns on the boosters, bursting to the edge, and tackles the ball carrier before he gets to the edge.

Vander Esch did an excellent job of targeting the running back's inside hip in his pursuit, effectively taking away the running back's ability to cut back once the rookie linebacker gets into range. It may seem basic, but far too many rookies (and even veterans) fail to show a firm grasp of the basic techniques. All too often, rookies get too excited and overrun the ball carrier, looking for a big hit.

Even though it's impossible to replace Lee, Vander Esch does bring more size and speed to the Cowboys defense.

Standing at 6-foot-4 and 256 pounds with 33 7/8-inch arms, Vander Esch is a linebacker trapped in a defensive end's body with the athleticism to match. Compare that with Lee, who is merely a good athlete with below average size (graphs found via Mockdraftable.com):

Sean Lee vs Leighton Vander Esch pic.twitter.com/1rTNneVHCr — John Owning (@JohnOwning) September 25, 2018

What many don't realize is that Vander Esch has one of the freakiest size-to-speed ratios in the NFL. He's a freak of nature in a physical and athletic sense, and it shows up on the field:

He doesn't get the tackle on this play but watch how the fullback looks like he hit a wall when he attempted to cut block Vander Esch. Seattle's fullback is listed at 235 pounds and has a running start, but Vander Esch doesn't even give an inch, which forces the running back to cutback into the teeth of the Cowboys defense.

Coming out of Boise State, one of Vander Esch's biggest concerns was his ability to take on, play through and defeat blocks against the run. Now he's not perfect there by any means, but if the Seattle game was any indication, Vander Esch will be just fine in that area:

Here, Vander Esch is essentially playing the "Mike" linebacker position while Dallas is in nickel personnel. The Seahawks are looking to horizontally stretch the Cowboys' front seven using an outside zone.

Once the ball is snapped, the Seahawks left guard is looking to seal or push Vander Esch passed the running back's alley. Yet, the rookie linebacker does an excellent job of mirroring the running back's steps while quickly flowing playside at a 45-degree angle toward the line of scrimmage, making it impossible for the left guard to get a clean block. The left guard resorts to a cut block attempt, which Vander Esch easily defeats in his pursuit of the ball carrier.

Vander Esch also displayed first-rate spatial awareness against the Seahawks. This play is a great example:

Here, Vander Esch is the "overhang" defender in Dallas nickel defense. Judging by the defense's alignment, the Cowboys were expecting the Seahawks to throw from their four wide receiver set; however, Seattle threw a change up and ran a zone concept toward Vander Esch's side.

After the ball is snapped, Vander Esch takes an initial step backward to start sinking into his zone before quickly identifying the run and beginning his pursuit of the ball carrier. Despite keeping his eyes on the running back the entire time, Vander Esch uses his peripheral vision to spot the tight end's block, which allows the Boise State product to easily side step the block, pursue the ball carrier and make the tackle behind the line of scrimmage.

He's not perfect by any means. In fact, Vander Esch needs to be more forceful when he initiates contact at the point-of-attack, whether it be defeating a block or bringing down a ball carrier.

Yet, it's rare to see rookie linebackers show an outstanding grasp of the fundamentals as Vander Esch has, and that's why the Cowboys defense won't see a noticeable drop off without Lee in the lineup.

It's the little things that separate the elite athletes from the elite football players, and while he entered the league as more of an athlete than football player, Vander Esch is becoming closer and closer to the latter by the day.

There are many reasons to be worried about this Cowboys team, but the defense's performance without Lee shouldn't be one of them.

You can thank Vander Esch for that.

John Owning writes about NFL player evaluation for SportsDayDFW.com. Follow him on Twitter at @JohnOwning.