The 63-year-old most notably led the Colts to a 14-2 record and an appearance in the Super Bowl in 2009, his first season as a head coach. After three years in Indianapolis, he spent four seasons with the Lions before being fired in 2017 after posting a 9-7 record.
Detroit has been much worse without him in 2018 under Matt Patricia; the Lions are 5-10 heading into Week 17.
Caldwell's experience, as well as his background as an offensive coordinator and quarterbacks coach, make him an intriguing option for the Packers.
Green Bay has an opening after firing Mike McCarthy earlier this month after 13 years with the organization. Joe Philbin has taken over on an interim basis and could be a candidate for the full-time job, although there will likely be a broad search to fill the role.
Charles Robinson of Yahoo Sports initially listed New England Patriots offensive coordinator Josh McDaniels as an option, while Albert Breer of The MMQB reported Northwestern coach Pat Fitzgerald has also been considered.