Being on injured reserve means Hurd will have to miss at least three games. That will make him eligible to return for Week 4 against the Seattle Seahawks.
The 49ers also activated cornerback Dontae Johnson from the practice squad to make him available for Sunday's game against the Detroit Lions. That could mean that starting cornerback Emmanuel Moseley (knee) is unlikely to be available. He was listed as "doubtful" on the team's official injury report.
On Wednesday, head coach Kyle Shanahan indicated that injured reserve was a possibility for Hurd.
"We felt pretty good going out of the Raiders game, just with how long he was able to play and get through it," Shanahan told reporters. "But [his knee] was hurting him three days later when we tried to practice again. We gave him the weekend off, and it was hurting again Monday. And just coming in here today [Wednesday], just realizing that we've got to re-evaluate this and shut him down for a little bit."
San Francisco made Hurd a third-round draft pick out of Baylor in 2019. He spent his first two NFL seasons on injured reserve.