SANTA CLARA -- Jimmy Garoppolo underwent surgery Wednesday morning to repair a torn anterior cruciate ligament in his left knee, 49ers coach Kyle Shanahan said.

Shanahan said it was too early to know if there was other damage to Garoppolo’s knee and when the quarterback would cleared to join the 49ers in their offseason program. Shanahan said he didn't know where the surgery was performed or the identity of the operating surgeon.

Garoppolo sustained the knee injury Sept. 23 at Kansas City, as he planted his left foot near the sideline in order to cut back inside at the end of a 13-yard scramble late in the 49ers’ 38-27 loss to the Chiefs.

The 49ers placed Garoppolo on injured reserve Sept. 26 and promoted quarterback Nick Mullens from the practice squad to take his place on the 53-man roster.

C.J. Beathard took over as the 49ers’ starting quarterback Sunday against the Los Angeles Chargers. He completed 23 of 37 passes for 298 yards and two touchdowns with two interceptions in the team’s 29-27 loss.