4 candidates who could replace Aaron Glenn as Lions defensive coordinator

Both of the Detroit Lions coordinators are lined up to top head coaching candidates as the 2025 hiring cycle approaches, and in a certain sense defensive coordinator Aaron Glenn feels more likely to leave for a head coaching job after this season than offensive coordinator Ben Johnson does.

The work Glenn has done with a continually injury-thinned Lions' defense this season is naturally bolstering his head coaching resume. He is lined up to have multiple opportunities if he wants them, but along the same line as Johnson it's safe to assume he'll be fairly selective and won't leave a good situation with the Lions just because he can.

Dan Campbell is also keenly aware he doesn't have a lot of time left with his coaching staff as it currently is, and he has feared losing Glenn to a head coaching job before. So it's fair to say Campbell has been/is preparing to lose Glenn after the season, whenever it ends for the Lions, and possibly vaguely considering who he might want as his new defensive coordinator.

Campbell hired a great staff upon becoming the head coach in Detroit, and he has made changes when needed. So he's not going to be caught off-guard by Glenn leaving, presumably with wide open communication from Glenn about head coaching opportunities he likes or doesn't like, and a replacement could be hired quickly if Glenn does leave.

If Glenn leaves for a head coaching job after the Lions' season is over, which an important emphasis on 'if', here are four possible candidates to be the next Lions' defensive coordinator.

4 possible candidates to replace Aaron Glenn as Detroit Lions defensive coordinator

4. Terrell Williams, Lions defensive line coach/run game coordinator

The litany of injuries the Lions have had along the defensive line this season have surely tested Williams as a coach, and look no further than the performance of Al-Quadin Muhammad on Thanksgiving Day against the Bears (five pressures, one sack) as a fresh testament of his ability to coach players up.

In a bit of an odyssey, given how long he's been in coaching, Williams has only been a defensive line coach and never a defensive coordinator. He did take on the extra title of assistant head coach under Mike Vrabel with the Tennessee Titans in 2023 though, and he was the head coach of one of the teams at the 2024 Senior Bowl.

As internal candidates to replace Glenn go, Williams might be No. 1 if not for someone else on this list.

3. Robert Saleh, former New York Jets head coach

Saleh was clearly not the biggest problem with the Jets this season, even if he was the first fall guy. Since he was fired after a 2-3 start to the season, the Jets are 1-5 entering Week 13 and their defense has been noticeably worse (25 or more points allowed four times in six games).

Saleh, a Dearborn, Michigan native, was in the mix for the Lions' head coaching job before Campbell was hired. Bypassing him proved to be a good decision, of course, but the issues the Jets' had during his tenure almost entirely lied with the offense and failing to find a suitable quarterback. And one offensive coordinator hire (Nathaniel Hackett) was hoisted on him to appease Aaron Rodgers.

Saleh is currently working as a consultant with the Green Bay Packers, and he will surely be in the mix for defensive coordinator posts after the season. If the Lions are in the market for a new one, he's an easy candidate.

2. Dennis Allen, former New Orleans Saints head coach

Allen was fired by the Saints after a 2-0 start this season became 2-7 record, and with a 26-53 record over parts of six seasons his days as a head coach are surely done. Overall, his fitness to be a head coach was easy to question at both stops he has had (the Saints and the Oakland Raiders).

What can't be questioned is Allen's acumen as a defensive mind. As noted by Al Karsten of Pride of Detroit, the Saints' defense improved dramatically over his tenure as the Saints' defensive coordinator (2015-2021) before he replaced Sean Payton as head coach. During Allen's two full seasons as the head coach (2022 and 2023), New Orleans had a top-10 scoring defense.

Allen's tie to Campbell from their years together as assistants under Payton in New Orleans could be meaningful if Glenn has to be replaced.

1. Kelvin Sheppard, Lions linebackers coach

Sheppard is a rising star on the Lions' coaching staff, with the makings of being a future head coach as he also works with a continually injury-thinned group. But he would likely have to become a defensive coordinator before that opportunity comes, and in that sense it's possible Glenn (or offensive coordinator Ben Johnson, if he takes a head coaching job) will want to take Sheppard with them elsewhere.

But until shown otherwise, Sheppard stands as the most likely next Lions' defensive coordinator whenever Glenn takes a head coaching job. You can bet Campbell will make every effort to keep his linebackers coach around as defensive coordinator if Glenn leaves, with most any other available option falling behind Sheppard in the pecking order.