The team has not formally announced the move, and it wasn't listed on the NFL's transaction report for Wednesday.
Avril has been sidelined since suffering a neck/spine injury in Week 4. He'll have to miss at least eight weeks while on injured reserve, and it's possible that he will miss the remainder of the season. Carroll has said that Avril's injury could be a long-term issue, and when asked last week if it could sideline him for the rest of the season, the coach didn't rule out that possibility.
Avril, 31, is in his 10th NFL season and his fifth with the Seahawks. He's coming off a career-high 11.5 sacks in 2016 en route to his first Pro Bowl appearance. He's signed through the 2018 season.
"He was a major part. He's a big piece of our puzzle," Seahawks defensive coordinator Kris Richard said Wednesday. "You hear the cliché time and time again, 'Next man up,' and it's just very difficult. It's very difficult, but we have to keep moving on, and we have to rely on the guys, [the] next man in line, and really, I think it's going to show who's been preparing."
Third-year defensive end Frank Clark, who produced 10 sacks as a rotational player last season, will continue to start in Avril's absence opposite Michael Bennett on early downs. Marcus Smith, Quinton Jefferson and Branden Jackson are the other defensive ends on Seattle's roster.
Jefferson has returned to practice since breaking his hand, but Richard said the team will need to evaluate him further to determine when he'll be able to play. Bennett didn't practice Wednesday because of what the team has called a plantar fascia foot injury, but he said he plans to play Sunday against the New York Giants.
Avril was injured in Seattle's Oct. 1 win over the Indianapolis Colts, when he dived to tackle Jacoby Brissett from behind and his chin landed on the back of the quarterback's cleat. Carroll referred to Avril's injury as a serious stringer but hasn't provided many specifics beyond that.
Carroll said on Tuesday that Avril is continuing to see specialists and that the team could learn more about his status over the next few days. Carroll is scheduled to speak with the media at large on Thursday.