Although he never used the word "retire," a series of tweets seemed to indicate he is moving on from the sport.
Gods Grace 🙏🏿🙏🏿🙏🏿 pic.twitter.com/60J2DugpD1— Kameron Chancellor (@KamChancellor) July 1, 2018
"To walk away from the game by choice is one thing, to walk away from the game because of the risk of paralysis is another," Chancellor tweeted.
The 30-year-old suffered a career-threatening neck injury last season and said in May that he would continue playing if his health permitted.
"If my body says don't play, I'm not playing. I'll listen," Chancellor told 13News Now in May. "I'm a very good listener."
On Sunday, Chancellor said the "final test" of his injury "showed no healing."
"I've played through all types of bruises and injuries at a high level. But this one, I just can't ignore," he tweeted.
Chancellor, a four-time Pro Bowler, missed the final seven games of last season after he was injured while making a tackle late in a November win over the Arizona Cardinals.
Known for his hard hitting as part of the Seahawks' famed "Legion of Boom" defense, Chancellor signed a three-year, $36 million extension last summer.
If Chancellor has indeed played his final down, it's unclear how the two sides might handle the situation procedurally. Chancellor's 2018 salary of $6.8 million became fully guaranteed in February, and $5.2 million of his $10 million salary for 2019 is guaranteed for injury. By retiring, Chancellor could potentially forfeit those guarantees, though the two sides could work out some sort of settlement.
It had seemed more likely than not that Chancellor had played his final down. Seahawks coach Pete Carroll said at the end of the season that Chancellor and defensive end Cliff Avril were going to "have a hard time playing football again." Avril also suffered a career-threatening neck injury last season and was released in May with a failed physical designation.
The team had no updates on Chancellor's status over the offseason, other than general manager John Schneider saying that Chancellor was scheduled to have another test in June or July that could provide some clarity on his football future. In his message, Chancellor said his "final test" showed "no healing," indicating that he has yet to be medically cleared to return to football.
The Seahawks clearly seemed to be preparing as though Chancellor weren't going to be available. They re-signed Bradley McDougald this offseason to a three-year deal after the versatile safety made two starts last season for Earl Thomas at free safety and the final seven at strong safety once Chancellor was injured. Seattle also signed Los Angeles Rams starting strong safety Maurice Alexander to a one-year deal, though he didn't participate much during the offseason program while recovering from a shoulder injury. McDougald would be an option to start at free safety should Thomas' holdout last into the season. Third-year safeties Delano Hill (strong) and Tedric Thompson (free) also worked with the first-team defense in the offseason, depending on where McDougald was playing.
A fifth-round pick out of Virginia Tech in 2010, Chancellor was one of several mid- to late-round gems that helped form the core of Seahawks teams that experienced new heights. The Seahawks made the playoffs five straight seasons from 2012 to '16, reached back-to-back Super Bowls and won the first championship in their history following the 2013 season. Chancellor made his share of memorable plays in the postseason, including a massive hit on Demaryius Thomas that set the tone for the Seahawks' 43-8 victory over the Denver Broncos in Super Bowl XLVII. He also had a pick-six of Cam Newton that sealed a divisional-round victory over the Carolina Panthers the following season.
Chancellor missed the first two games of the 2015 season -- both Seattle losses -- while holding out. He returned without a new contract or any money added to his existing deal and played two seasons before the Seahawks gave him a three-year extension in the summer of 2017.
ESPN's Brady Henderson contributed to this report.