Hightower, who has been limited with a hamstring injury, will miss his second straight game. His top backup, Tracy White (foot), is also out, so the Patriots are thin on the strong side.
One possibility is defensive end Rob Ninkovich moving to that spot.
Hightower is a strong player against the run, which figures to be a top priority on defense against the Seahawks, who rely heavily on Marshawn Lynch. Getting Lynch going is crucial for the Seahawks, who start rookie Russell Wilson at quarterback.
Edelman wasn't expected to play.
Meanwhile, tight end Aaron Hernandez (ankle) has made the trip to Seattle, putting him in position to play.