Per Schefter, the "belief around the league" is that Thomas will sit out training camp and possibly part of the regular season unless he is traded or receives a new contract.
ESPN's Chris Mortensen reported Wednesday that Thomas would not report for the start of training camp. Mortensen added that Thomas' decision meant there would be "zero chance" of an extension.
The 29-year-old has spent his entire, eight-year NFL career with the Seahawks.
In addition to being a one-time Super Bowl champion, Thomas is a six-time Pro Bowler and three-time All-Pro First Team selection.
Thomas recorded 88 tackles, six pass breakups and two interceptions in 14 games last season.
It first became apparent last season that Thomas may be unhappy in Seattle.
After a December win over the Dallas Cowboys, Thomas entered the Cowboys locker room and told head coach Jason Garrett, "If y'all have the chance, come get me," according to Jon Machota of the Dallas Morning News.
Thomas is an Orange, Texas, native who played his college football at the University of Texas.
With Richard Sherman now a member of the San Francisco 49ers and Kam Chancellor's likely retirement, Thomas is the final holdover from the vaunted Legion of Boom secondary that helped carry the Seahawks to two Super Bowl appearances.
Thomas is set to earn $8.5 million base salary in the final year of his contract in 2018 before hitting free agency, per Spotrac.
The Seahawks missed the playoffs for the first time since 2011 last season, and they appear to be in transition with the departures of so many key players in recent years.
Quarterback Russell Wilson may be the face of the franchise, but Thomas has long been one of the team's most important leaders, and proceeding without him would leave a massive void on the Seattle defense.