Sherman's reserve stint isn't expected to last much longer than three weeks, according to Ian Rapoport of NFL Network.
It's unclear when exactly Sherman sustained the injury, but he was replaced by Ahkello Witherspoon on the final defensive drive of San Francisco's opening-week loss to the Arizona Cardinals.
Sherman, 32, returned to Pro Bowl form last year while helping the 49ers reach Super Bowl LIV. He finished the 2019 campaign with 11 pass breakups and three interceptions while adding two more picks in the playoffs.
A five-time Pro Bowler, Sherman was one of the game's most dominant cornerbacks over his seven-year run with the Seattle Seahawks before signing with San Francisco in 2017.
The 49ers will travel across the country to face the New York Jets in Week 2.