Soon after, the Niners ruled out a return for Mostert, as he watched the end of the game from the sideline. Coach Kyle Shanahan said after the game he didn't have any update on Mostert but that he expected him to have further evaluations on Monday.
"We don't know yet on Raheem," Shanahan said. "I'm sure we'll find out tomorrow. I'm sure he tried to come back, I know he did at the end of the second quarter, he tried to come back again, I think he did one play in the third quarter and then he couldn't go."
Mostert, 28, suffered the injury late in the second quarter and hobbled to the sideline before halftime. During the intermission, Mostert got additional tape put on the ankle and tested it on the first play of the second half, running for a 1-yard gain.
But Mostert went back to the sideline and made his way to the bench, where he was seen limping.
Before his departure, Mostert was heavily involved in the offense, carrying 17 times for 65 yards with two catches for 11 yards before departing with the injury. Jerick McKinnon initially stepped in for Mostert after the injury but the team turned to rookie JaMycal Hasty for a late spark to help seal the 24-16 victory.
Hasty finished with nine carries for 37 yards and helped drain the clock late with some first-down runs.
"I thought he did a real good job when he came in," Shanahan said. "Hasty was up for the challenge, got some fresh legs in there and I thought he gave us some juice a little bit. ... Hasty got his opportunity and from what I saw, I thought he really helped us."
Earlier this season, Mostert missed two games with a sprained knee suffered in a Week 2 win against the New York Jets. He returned from that injury last week against the Miami Dolphins. Since the Niners were without Jeff Wilson Jr., who was inactive because of a calf injury, it left Hasty and McKinnon as the only healthy tailbacks on the roster.
Elsewhere on the injury front, 49ers center Ben Garland (calf) and safety Jaquiski Tartt (groin) exited in the second half and did not return. They, too, will have further evaluations before a determination on their status for next week is made.