Under the NFL's adjusted rules, Sherman will miss at least the next three weeks. The earliest he could return would be for the 49ers' Week 5 game against the Miami Dolphins on Oct. 11.
49ers head coach Kyle Shanahan said the hope is that Sherman's calf injury won't keep him out any longer than the three-week minimum.
"He doesn't sound too concerned about it," Shanahan told reporters Wednesday. "He just is going to need a couple weeks we think, and maybe a little bit more. But hoping it's only three. That's why we put him on IR."
Sherman played 78 of the team's 82 defensive snaps in the 49ers' loss to the Arizona Cardinals on Sunday. The four snaps Sherman missed came at the end of the game when the Cardinals were kneeling to run out the clock.
The loss of Sherman leaves the 49ers short-handed in the secondary. Along with Sherman's injury, veteran Jason Verrett is dealing with a hamstring issue and Ahkello Witherspoon -- the top candidate to replace Sherman -- is in the concussion protocol.
After putting Sherman on IR, the 49ers had only two healthy cornerbacks -- Emmanuel Moseley and K'Wuan Williams -- on the roster. Later Wednesday, the team promoted cornerback Dontae Johnson to the active roster and signed cornerback Ken Webster from the Dolphins' practice squad.
The 49ers play the New York Jets on Sunday in Week 2 of the NFL season.