The San Francisco 49ers couldn't escape the injury bug during the team's exhibition opener against the Dallas Cowboys on Thursday night. Linebacker Malcolm Smith (hamstring), tight end George Kittle (shoulder), defensive lineman Solomon Thomas (head injury), tackle Garry Gilliam (head injury), and linebacker Eli Harold (leg) all sustained in-game injuries and did not return.

Also on the injury list was running back Matt Breida, who is expected to have a prominent role as Jerick McKinnon's backup. He had just one carry for three yards before exiting the game with a shoulder injury.

"I know it's going to be some time," head coach Kyle Shanahan said on Thursday night. "So, I don't know how long, but I have a feeling it's going to be some time."

The loss of Breida would be a significant one for the 49ers offense, but it does create a bigger opportunity for those fighting for the team's coveted third running back job. Among those players is second-year running back Joe Williams, who has impressed during training camp after spending all of his rookie season on injured reserve.

Williams, along with Raheem Mostert and Jeremy McNichols, will see increased reps in practice and the preseason if Breida cannot return soon.

"I thought they ran hard," Shanahan said of his backup running backs after the game. "I don't think we gave them a ton of space today. The times that we did have space, I thought they made some good runs. Then Jeremy (McNichols) came in and made some also. But, I did not think there was a lot of space in the game from what I saw.

"I know Raheem had that fumble, which it's tough for me to see. I couldn't tell on the replay, and I didn't see it live, so I'm not sure how that played out. But, I was happy with how hard they ran. It didn't seem like they left much out there."

Shanahan wants a chance to get a good look at all of the running backs during the preseason. The 49ers were rotating between Mostert and McNichols during much of the second half against Dallas.

"We try to balance it up throughout the whole preseason where we get a chance to see all the running backs," Shanahan said.

The 49ers will hold practices on Sunday and Monday before traveling to Houston where they will take part in two joint practices with the Texans before the teams' August 18 matchup.