49ers running back Elijah Mitchell underwent an MRI on Monday to determine the full extent of his knee injury.
Mitchell has a sprained medial collateral ligament that will sideline him about two months, Adam Schefter of ESPN reports.
Mitchell injured his knee in the second quarter after 17 snaps. He had six carries for 41 yards, and quarterback Trey Lance ended up leading the team in rushing with 13 carries for 54 yards.
The 49ers also have Jeff Wilson Jr., Jordan Mason and Tyrion Davis-Price on their 53-player roster at running back.