ALLEN PARK, Mich. -- The search is officially on for Detroit's next head coach.

ESPN Insider Chris Mortensen is reporting Penn State coach Bill O'Brien might already be coming off the board to Houston, but there are other attractive candidates out there for the Lions.

“I think this is a very attractive opportunity,” Lions president Tom Lewand said. “I can verify that by the number of calls we've already gotten since the announcement was made at noon today and it will go through the process. I think going through a thorough process is extremely important.

“But that doesn't necessarily mean it has to be a long process, but it has to be a thorough process and we will go through a process of interviews, of research to make sure that we find the best fit for the Detroit Lions.”

While Detroit would not identify candidates Monday, here are some names that could pop up in the search based off of the criteria Lewand and GM Martin Mayhew laid out Monday afternoon.

Ken Whisenhunt, San Diego offensive coordinator: It would be surprising if he isn't one of Mayhew's top candidates. The two were teammates in Washington in 1989 and 1990. He is primarily an offensive guy and has worked with both Ben Roethlisberger in Pittsburgh and Philip Rivers last season. He also has prior head coaching experience, running the Arizona Cardinals from 2007 to 2012 -- and taking the Cardinals to Super Bowl XLIII. If a coach can take Arizona to the Super Bowl, he could fit well in trying to take the Lions to the next level.

Lovie Smith, former Chicago Bears head coach: Smith has all the characteristics Mayhew would want in a coach. He runs a 4-3 defense, which would fit well with what the Lions already have assembled. He has head coaching experience, having led the Chicago Bears from 2004 to 2012. He knows how to build culture as he has taken a team to the Super Bowl and would be a strong hire for the Lions. However, Insider Adam Schefter is reporting Smith is the favored candidate in Tampa Bay.

Jay Gruden, Cincinnati offensive coordinator: He helped in the development of Andy Dalton over the past three seasons and understands the importance of a strong quarterback-wide receiver combination as he worked with Dalton and A.J. Green. He doesn't have NFL or college head coaching experience, but was the head coach of the Orlando Predators of the AFL from 1998 to 2001 and the Florida Tuskers of the UFL in 2011. So he has some experience somewhere leading a team.

Hue Jackson, Cincinnati running backs coach: Jackson has head coaching experience from his 2011 season with Oakland. He's a former quarterback (University of the Pacific) who has been an offensive coordinator for years on the college and professional level.

In Baltimore in 2008 and 2009, he tutored Joe Flacco and worked with Carson Palmer as the offensive coordinator at USC.

Mike Zimmer, Cincinnati defensive coordinator: Zimmer has been a defensive coordinator in the NFL since 2000 and has spent a lot of time building playoff defenses, something the Lions have shown they have the pieces to build.

The concern here would be the lack of any head coaching experience or any experience on offense, which is a problem considering the struggles of Matthew Stafford. Mayhew indicated experience on a particular side of the ball would not be a huge factor.

Adam Gase, Denver offensive coordinator: The 35-year-old could be a wild-card hire. He doesn't have head coach experience, but worked with Peyton Manning both as a quarterbacks coach and as offensive coordinator. He was born in Ypsilanti, Mich., and went to Michigan State.

He scouted with the Lions from 2003 to 2005 and was a coach in various roles from 2005 to 2007.

Brian Kelly, Notre Dame head coach: He didn't have the best year last year, but he flirted with the NFL last season and the Lions are a team that could win immediately. He has an offensive pedigree, head coaching experience at one of the most pressure-packed jobs in college football and has elevated every program where he has coached. He could be a decent definition of a coach that can push a team over the hump.

The concern would be his lack of NFL experience.

David Shaw, Stanford head coach: If there was the thought Shaw would actually leave Stanford, he might be the top coach on this list. He has an offensive pedigree as an offensive coordinator with the Cardinal. He has extensive NFL experience grooming quarterbacks in Oakland and Baltimore before latching on with Jim Harbaugh. He has ties to the Lions as his father, Willie Shaw, was the defensive backs coach for Detroit from 1985 to 1988 and he spent part of his high school career in Michigan. He'd be the perfect candidate except for this -- will he leave Stanford?

Here's what he said about the NFL on Monday:

“I haven't been contacted by anybody. To be honest it's unbelievably flattering. I think it's really cool,” Shaw said. “I think honestly it continues to shed light on our program, so I don't mind that it keeps happening. It keeps eyes turning toward Stanford, which I think is really cool. I told our players, to be honest, it's a testament to what they've accomplished, it's a testament to what our seniors have helped build at Stanford, to win consistently, win the right way, produce high-character young men and have a football game that's exciting to watch.

“So I don't mind it. I have no desires to pursue another job. As I said, I have not and don't plan on interviewing with anybody. I think it's really nice that my name gets batted around and that's great, and part of it is because I do have nine years of NFL experience, so it seems like an easy transition for some people.

“But honestly I'm looking forward to playing this game and getting into the offseason and starting to put together another winning season next year.”