NOTE:This is a constantly updating list of candidates for the 2018 Cincinnati Bengalshead coaching position.

The idea that Marvin Lewis would not be the head coach of the Cincinnati Bengals in 2018 wasn’t a foreign one to ownership inside 1 Paul Brown Stadium. You don’t let a head coach and his entire coaching staff head into a season in the final year of their deals without a “list.”

The Bengals have theirs.

If the search for the 10th head coach in franchise history indeed begins this week, here is the BX list of potential candidates, culled from sources that have a pulse on both inside PBS and around the league:

Outside candidates

BX has learned who won’t be in play for the Bengals: Jon Gruden (should he decide to return to the sideline), New England offensive coordinator Josh McDaniels and Minnesota offensive coordinator Pat Shurmur. BX believes they will have opportunities elsewhere that they find more appealing, for a variety of reasons.

That leaves the pickings thin for offensive minds but each of the following names would (or should) be considered not just in Cincinnati, but for any of the potential six to nine potential openings come the new year.

So, if the Bengals decide to totally move in a new direction, here ones to consider:

Matt Nagy, Kansas City offensive coordinator

Like any coordinator with a strong head coach, Nagy will have to prove just how much input he had in the Chiefs offense under Andy Reid – but Nagy was given a lot of credit for how successful the Chiefs offense was during their 5-0 start and in adjusting late in the year to help get the Chiefs rolling again heading into the playoffs. Alex Smith turned into a Pro Bowler with Nagy as his position coach and was early MVP candidate this year, which will make Nagy a compelling candidate for teams like the Bengals who feel they have a veteran quarterback in place.

Update: Reports have Nagy being on the list to be interviewed in Indianapolis.

Mike Vrabel, Houston defensive coordinator

The Akron native and Ohio State alumnus is a rising star in the business after a 14-year playing career that featured three Super Bowl victories. He went from coaching the Buckeyes linebackers to coaching that position in Houston in three years, and then just two years later San Francisco wanted him as their DC. Houston stepped up and promoted him, and he's clearly on the radar for teams as a quick-riser.

Update: Detroit has asked permission to speak to him and the Colts will speak to him as well.

Kris Richard, Seattle defensive coordinator

A former defensive backs coach who molded the famed "Legion of Boom," Richard has been calling the Seahawks' defense since 2015, and he kept that unit at the top of the league in 2015 and 2016 and has managed to keep it effective this year despite losing almost the entire secondary due to injury, as well as managing injuries up front.

Update: The Colts are casting a wide net, and have sought to interview Richard as well.

Frank Reich, Philadelphia offensive coordinator

The former Buffalo Bills backup quarterback is on his second turn as a play-caller, after spending 2014-15 in San Diego before being dismissed. He has been with Eagles head coach Doug Pederson the last two seasons and the team improved from 16th in scoring last year to one of the best in the league this year. They have also improved from 22nd on offense into the top three, and he’s proven he’s willing to hand the ball off. He also had one year with a top 10 offense in San Diego.

Harold Goodwin, Arizona offensive coordinator

He seems primed for a head job at this point after coordinating the Cardinals offense under Bruce Arians since 2013. Arians brought Goodwin with him from Indianapolis, where Goodwin coached the offensive line. With Carson Palmer, Goodwin's group peaked at No. 1 overall in the league in 2015. He interviewed with three teams before the start of last season.

Jim Caldwell, former Detroit head coach

Caldwell, 62, was fired on Jan. 1 after going 9-7 for the second straight year with the Lions. In four seasons at the helm in Detroit, he posted a 36-28 record and three winning seasons. In three years as the head coach of the Indianapolis Colts, he went 26-22. He took both franchises to the playoffs for a career postseason mark of 2-4. Those two wins came in 2009 when the Colts lost to the New Orleans Saints in Super Bowl XLIV. Caldwell was also the Baltimore Ravens offensive coordinator when the Ravens won Super Bowl XLVII. Despite being known as an offensive-minded head coach, he had just two top-10 offenses (2009-10) and three top-10 scoring offenses (2009-10, 2017). He also never had a rushing attack ranked better than 26th.

Others to monitor: Mike Munchak, Pittsburgh offensive line coach; John DeFilippo, Philadelphia quarterbacks coach

Update: Chicago has asked to interview DeFilippo for their open position.

Internal candidates

Darrin Simmons, special teams coordinator

Simmons has also been with Lewis and the club since 2003, and he was the one tabbed to head practice for Lewis when the head coach missed time in training camp with a health issue. By nature of the position has Simmons working with offensive and defensive players for years bringing them together, including starters.

Paul Guenther, defensive coordinator

Guenther has been with the Bengals for 13 years and is in his fourth as defensive coordinator. He has experience on the offensive side of the ball in his early days with Washington, has coached special teams and is the latest of Lewis’ coordinators to find himself on the radar within the league. He was blocked by the Bengals from heading to Washington to start this season and there is a strong feeling that should he not be the next Bengals head coach he will be elsewhere in 2018.

Update: Guenther has already been linked to Oakland as Jon Gruden's defensive coordinator should the former Super Bowl-winning head coach return to the sidelines.

Bill Lazor, offensive coordinator

Promoted to the play calling position after Week 2, Lazor has proven to be detailed and thoughtful and some in the organization believe he has the makeup to be a head coach. Having now called plays for two organizations and with a strong coaching background, Lazor should impress in interviews.

College head coaches

BX believes the Bengals will focus in on NFL talent first should they be looking for a head coach, but they will not ignore the college ranks once the coaching carousel begins. Hot names are Stanford’s David Shaw and Michigan’s Jim Harbaugh, but BX believes Shaw isn’t ready to leave and Harbaugh has said he is not returning to the NFL this season. Here is a preliminary list of college coaches to keep an eye out for as possible interview candidates:

Brian Brohm, Purdue head coach

Brian Kelly, Notre Dame head coach

Matt Campbell, Iowa State head coach

The future of Bengals’ assistants

While the three coordinators will get their chance to interview should Lewis and the team part ways, that leaves an entire coaching staff wondering about their future.

But many won’t be looking for work long. In fact, some may be in line for greater roles either with a new head coach here in Cincinnati, with Lewis if he coaches in a new city, or elsewhere in the league. Here’s a quick look at the rising stars on the current staff and where they may project to in 2018:

James Urban, wide receivers coach

Urban is the new Mike Zimmer in that he’s had to wait too long to get a shot at the next level, and in Uban’s case that is calling plays as an offensive coordinator. Urban was with Andy Reid in Philadelphia from 2004-10 and coached Pro Bowl quarterbacks there, and he has been with Lewis here since 2011 and coached a Pro Bowl receiver. He knows the inner workings of a successful offense and has a personality that connects with players. He should be interviewing for OC spots this offseason at the very least.

Kyle Caskey, running backs coach

Say what you want about individual running styles, it’s hard to argue with the production and season-long improvements of this group under Caskey. He has experience coaching on the offensive line and tight ends and could have future at either of those positions as well going forward.

Brayden Coombs, special teams assistant

As Darrin Simmons’ right-hand man, Coombs is well thought of around the league and should be in line to jump to a coordinator position. With a revolving door of personnel this season the Bengals couldn’t unveil a lot of different looks on special teams, but Coombs will be able to impress in interviews with schemes and he will immediately be able to connect with a room of players.

Rob Livingston, co-secondary coach

The former scout should be a hot commodity for his personnel background as well as his ability to connect with his players. Another fast riser in the league, Livingston is positioned to command an entire secondary room and may be a dark horse defensive coordinator candidate if the right college job opened.