Kyle Williams is expected to open the season as the 49ers' punt returner, as LaMichael James sustained a knee injury Thursday night that is estimated to keep him out of action for three weeks.
James sustained a sprain to the medial collateral ligament in his left knee in the team's exhibition finale against the San Diego Chargers, a source said Friday morning. The injury will not require surgery.
James had two punt returns for 10 yards and handled three fair catches during the 49ers' four exhibition games. The team's third-string running back carried 24 times for 55 yards.
Perrish Cox, who has a strong chance to make the 49ers' 53-man roster as the fifth cornerback, was the most productive punt returner this summer with 36 yards on three returns. Receiver Chad Hall, a player on the bubble, returned three punts for 18 yards.
Williams opened last season as the 49ers' punt returner when Ted Ginn was unavailable due to an injury. Williams had four returns for 52 yards (13.0 average) and had six fair catches before Ginn resumed his role as the return specialist. Ginn signed a contract with the Carolina Panthers in the offseason.
Williams did not play in any of the 49ers' exhibition games this summer after returning to the practice field from a torn left ACL that ended his 2012 season. But Williams is expected to be ready to play when the 49ers open the season Sept. 8 against the Green Bay Packers at Candlestick Park.
Williams is also available to replace James on kickoff returns. Rookie Quinton Patton and Cox returned kickoffs in the exhibition season. Receiver Lavelle Hawkins, who is on the bubble for a roster spot, had a 105-yard touchdown return a week ago against the Minnesota Vikings.