"That looks to be a significant injury," Raiders coach Dennis Allen said after the game. "We'll find out more later."
Branch was injured rushing Jaguars quarterback Chad Henne on a third-and-7 play in the first quarter and was in the offensive backfield when he needed to be helped off the field.
"I just saw him in the trainer's room, all iced up," Young said of Branch. "I just told him to stay up."
Branch is one of just two returning starters on defense, along with defensive end Lamarr Houston.