Thurmond was placed on season-ending injured reserve, joining veteran Marcus Trufant, whom Thurmond replaced in the starting lineup after Trufant was lost with a back injury before Week 5.
Thurmond suffered the fracture when he broke up a pass during the second quarter of Sunday's 6-3 loss at Cleveland and was landed on. He also suffered a high ankle sprain, but the extent of that injury wasn't known until Monday when it was found that Thurmond suffered significant ligament damage that will require surgery later this week.
The expected recovery time on Thurmond is four to six months. Rookie Richard Sherman will move into the starting lineup in Thurmond's spot.
"It's legitimately a long time of recovery," Carroll said. "... This is going to be a long haul."
Thurmond, a second-year pro out of Oregon, missed most of his senior year with the Ducks after suffering a major knee injury. Sunday's game in Cleveland was his fourth NFL start.
Thurmond's was the only significant injury suffered during the loss for Seattle. The other major injury happened during pregame warmups when lower back spasms locked up running back Marshawn Lynch.
"We were surprised by that, that it popped up and became such an issue," Carroll said. "We're going to have to be careful how we project this right now because he was OK going into game day. He had some symptoms, but this kind of jumped at us. We'll have to be careful with him through the week."
Quarterback Tarvaris Jackson, tight end Zach Miller and center Max Unger are the other unknowns for the Seahawks, who host the Cincinnati Bengals this weekend. Jackson (pectoral) went through pregame warmups Sunday but was inactive for the game, and Carroll said it will be later in the week before the team knows if the quarterback can play against the Bengals.
Copyright 2011 by The Associated Press