Coach Pete Carroll announced the news Friday. He expressed confidence that Carson, Seattle's leading rusher in each of the previous three seasons, will play next year.
"We went as long as we could and he worked as hard as he could at it and ... after not being able to get it to happen, to turn around, this is the best choice we've got," Carroll said. "So we'll look forward to him getting all that taken care of and be ready for a big year next year."
It's another blow to the 3-6 Seahawks but not an unexpected one. Carson's prospects for a return this year have been in question for a while, and Carroll signaled earlier in the week that his season could be over when he hadn't made the progress Seattle had hoped.
Alex Collins is expected to remain Seattle's starter, a role he has filled since Week 5.
Collins (groin) was again on the injury report this week but is "ready to go" for Sunday's game against the NFC West-leading Arizona Cardinals, according to Carroll. Strong safety Jamal Adams (groin) and cornerback D.J. Reed (groin/knee) are listed as questionable and will be game-time decisions, Carroll said.
Carson, 27, hasn't played since his neck began bothering him after Seattle's win over San Francisco in Week 4. He was placed on injured reserve Oct. 15 and was designated for a return to practice last week. He practiced last Wednesday and Thursday but not Friday. He didn't practice this week.
"We had time, so we took as much time as we could to rest him and then we built him up to bring him back, and then when he came back to practice the first day, it wasn't quite right," Carroll said Friday. "He practiced again the next day, and it just didn't relent. It's been real uncomfortable for him. It's been physically uncomfortable for him."
Carroll described Carson's injury as a "little spot" in one of his vertebrae "that's irritating the nerve." It's different than the neck injuries that ended the careers of former Seahawks Kam Chancellor and Cliff Avril, Carroll said. He answered in the affirmative when asked if that gives him hope that Carson will return.
It's unclear how long Carson's neck injury has been an issue. Carroll initially described it as an old condition that Carson aggravated but said Friday that it didn't bother him in previous years.
"He's an avid, avid weightlifter and he puts a ton of weight on his shoulders and it's right up there," Carroll said. "Who knows, it could have come from anywhere. But it's a wear-and-tear type of thing that developed. He has not had signs of it from the past."
Carroll said surgery would have been a consideration this offseason had Carson been able to continue playing and that doing so now gives him a head start on his rehab.
Carson is under contract through 2022 after testing free agency this past offseason and returning to Seattle on a two-year, $10.425 million deal. It included $5.5 million guaranteed and an artificial year in 2023 that automatically voids.
"That's the whole reason that we're doing it now," Carroll said after reiterating his confidence that Carson will be back in 2022. "He's all for it. We just couldn't shake it. Tried like crazy to get it done. But this is so that he can play next year."
Carson has rushed for 3,502 yards and 24 touchdowns since the Seahawks drafted him in the seventh round in 2017. He topped 1,100 yards in 2018 (14 games) and 2019 (15 games), the two healthiest seasons of what has otherwise been an injury-marred career. He missed 12 games as a rookie and four last year.
He rushed for 232 yards and three touchdowns in four games this season.
"We've been kind of dealing with it for some time, so we've had to be prepared to move on," Carroll said. "But Chris has been one of my favorite guys for a long time around here, ever since we found him and drafted him and all the style and the toughness that he's brought to us. He'll always be one of my favorite guys. Looking at that big 32, there's just something about the way he carried it that we obviously have missed all season and we'll miss. But we've got to ... take care of him. We've got to get him right."
Carson's injury has opened the door for Collins to resurrect his career in his second stint with Seattle. He has rushed for 345 yards and a pair of touchdowns in eight games, starting all five since Carson went down.
The Seahawks also have Rashaad Penny, Travis Homer and DeeJay Dallas at tailback. Penny has played behind Carson in three-plus injury-filled seasons since Seattle drafted him 27th overall in 2018. He didn't play a snap last week against Green Bay.
"I'm really looking forward to Rashaad, really looking forward to seeing where he goes and contributes this week," Carroll said. "He's got a real good role for us, and we're anxious to see him get going. ... It's really his time to help us. As we go through the next couple weeks, you'll see him continue to be a big part of it."
Left tackle Duane Brown (hip) practiced Friday and is OK, according to Carroll. He doesn't have a game designation, indicating that he is healthy enough to play.
Adams and Reed were hurt in practice this week. Neither practiced Friday.
"We don't know enough about it yet, so we've got to wait and use every day," Carroll said. "They're hopeful that they're going to be all right."
The Seahawks listed defensive end Kerry Hyder Jr. (calf) as questionable, but he practiced Friday as a limited participant and "feels good," Carroll said. Also listed as questionable were offensive linemen Jamarco Jones (back) and linebacker Cody Barton (quad), both backups.