The eight-year veteran left last week’s game against Arizona with a neck injury on the Cardinals’ final possession. Coach Pete Carroll said earlier this week that Chancellor suffered neck stingers but was still undergoing testing.
The NFL Network was first to report Saturday that Chancellor likely would miss the rest of the season because of the neck injury.
Chancellor, who has 49 tackles and a forced fumble this season, did not practice Thursday or Friday. The hard-hitting safety has 12 career interceptions and has been elected to four Pro Bowls.
Bradley McDougald, who is Seattle’s primary backup at both safety spots and has started the past two games at free safety, would start for Chancellor at strong safety against the Atlanta Falcons on Monday night.
The Seahawks (6-3) are one game behind the NFC West-leading Los Angeles Rams and are currently the sixth seed in the NFC playoff standings — one game ahead of four teams.
Seattle’s secondary already is without Pro Bowl cornerback Richard Sherman, who suffered a ruptured Achilles tendon in last week’s victory over Arizona and is out for the season. Star safety Earl Thomas is expected back this week from a hamstring injury.
ESPN’s Brady Henderson contributed to this report.