Defensive lineman Junior Siavii also suffered a neck stinger after a hard collision with Atlanta running back Michael Turner in the fourth quarter, coach Pete Carroll said. Siavii was on the field for a few moments before getting up and jogging off.
Carroll said Trufant's back would not "settle down" to where he could go back in. Trufant eventually returned to the sideline in the fourth quarter still in uniform but without his helmet.
Trufant missed the first six games of the 2009 season with a back injury.
Trufant left on Atlanta's final drive of the first half. He was replaced by Kennard Cox, because Walter Thurmond -- the usual backup cornerback -- was inactive Sunday with a hamstring injury.
Copyright 2010 by The Associated Press