Per Matt Maiocco of NBC Sports Bay Area, Foster injured his right ankle while making a tackle in the first quarter. Matt Barrows of the Sacramento Bee noted a cart was used to take Foster off the field.
After the game, coach Kyle Shanahan said the "initial worry" is a broken tibia, but X-rays came back negative, per Barrows. "It's not that horrible," said Foster, per Casey Pratt of ABC 7. "I'll be back soon. Very, very, very soon."
The Niners selected Foster with the 31st overall pick in the 2017 NFL draft. The Alabama product racked up 211 total tackles and seven sacks across three seasons with the Crimson Tide, including 115 tackles and five sacks during a standout 2016 campaign.
The 23-year-old Butkus Award winner appeared in all 30 of the Tide's games during his final two years in college. He underwent shoulder surgery in February, however, and he dealt with a different shoulder problem during training camp.
San Francisco may use a committee approach to fill the void alongside NaVorro Bowman and Eli Harold if the first-year starter misses additional time. Ray-Ray Armstrong, Brock Coyle and Dekoda Watson could all see snaps at weak-side linebacker.
But none of the reserve options possess the same upside as Foster, which could lead to issues for the 49ers. As for Foster, injuries have become a concern as he attempts to establish himself in the NFL.