Thornton (concussion) has been ruled out ahead of Sunday's game against the Broncos, Ryan McFadden of ESPN.com reports.
Thornton suffered a concussion in the Raiders' Week 13 loss to the Chargers and couldn't practice at all during the week. That suggests he hasn't made much progress through the league's concussion protocol. Jack Bech is expected to have a chance to step up in Thornton's absence.