He suffered the injury last season during a 23-12 loss to St. Louis. Simmons had been in the midst of an outstanding season despite missing two games in October with a shoulder injury.
In addition to losing Simmons, Seattle will not have the services of backup linebacker Tracy White for the next two weeks. He is suffering a strained right hamstring.
Linebacker Chad Brown is also questionable for Sunday's game against Miami with a strained left knee.