Bears quarterback Justin Fields won’t practice Wednesday, head coach Matt Eberflus said, and remains doubtful for Sunday’s game against the Raiders.

Rookie Tyson Bagent will start Sunday against the Raiders and veteran Nathan Peterman will be the second-stringer.

Fields is working with Bears trainers after dislocating his right thumb when his throwing arm was slammed into the ground on a sack in the third quarter Sunday. Fields tried to lobby to return to the game but couldn’t grip the ball with his right hand.

Thumb dislocations are accompanied by tears in the ligaments surrounding the thumb. It’s unclear if Fields will need surgery to fix the tears or if the team will let it heal on its own. Coach Matt Eberflus said the Bears will monitor Fields throughout the week and make a decision then.

If the Bears put Fields on injured reserve he’d have to miss the next four games.

The Bears signed quarterback Trace McSorley on Tuesday, indicating they did not expect Fields to practice this week. McSorley will run the practice squad offense.