Garoppolo did not participate in Wednesday's practice but turned in limited sessions on Thursday and Friday.
Garoppolo played in every snap in Week 3 against the Steelers. A few moments after the game, Garoppolo was evaluated for concussion symptoms and Vegas placed him in protocol the next day.
The Raiders will be short handed on defense as linebacker Curtis Bolton (knee) and cornerback Nate Hobbs (ankle) have been ruled out for Week 4. Defensive end Maxx Crosby is questionable to play due to a knee injury.
Over his 15-year career, Hoyer has a 16-24 record as a starter and is familiar with head coach Josh McDaniels' system with their time in New England. Meanwhile, O'Connell had little NFL experience during the preseason, where he showed some flashes and delivered accurate passes under center.