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.
Tight end Aaron Hernandez made the trip with the team to Seattle and is in position to play, but the Patriots have not yet said whether or not he will play.
Hernandez has been out since Week 2 with an ankle sprain. The Boston Globe reported that if Hernandez does return Sunday, it will be in a limited role.