SANTA CLARA - With 49ers running back LaMichael James spraining his knee in Thursday night's preseason finale, Kyle Williams probably will return to punt-return duties in the Sept. 8 season opener against the Packers.
James, the team's primary punt returner in the preseason, went to the sideline in the second quarter and iced his left knee during the rest of the first half.
The injury is a Grade 2 sprain of his medial collateral ligament, which typically requires three or four weeks of recovery. James was seen limping after the game.
A 2012 second-round pick, James was the team's No. 2 running back behind Frank Gore throughout the offseason as Kendall Hunter rehabilitated from an Achilles' injury suffered late last season. James had 24 carries for 55 yards (2.3 average) during the preseason.
Hunter, back at full strength, started Thursday's game against the Chargers at tailback while Gore took the evening off.
James was inactive for the first 12 games of his rookie season. However, he gave the team a spark following Hunter's injury.
James averaged 4.6 yards per carry in the final four regular-season games and 5.9 yards in the postseason and Super Bowl. He also handled kickoff returns, averaging an impressive 29.8 yards in the regular season.
Williams, meanwhile, is best known for two critical punt-return flubs in the 2012 NFC Championship Game, which the 49ers lost to the New York Giants in overtime. He handled 10 punts - six of them fair catches - last season without any miscues.
James also was listed as the top kickoff returner on the 49ers' offseason depth chart.
Rookie wide receiver Quinton Patton handled the first two kickoff returns against the Chargers. Patton, Hunter, Perrish Cox or Williams is capable of handling those duties in James' absence.
Another wide receiver, Lavelle Hawkins, returned a kickoff 105 yards for a touchdown in the third week of the preseason against Minnesota. He also had a 33-yard return in the second half against the Chargers.
Hawkins is one of the players on the 49ers' roster bubble. They must trim it to 53 players by 3 p.m. today.
Meanwhile, quarterback Seneca Wallace, who did not travel with the team to San Diego on Thursday, has no immediate plans to retire, his agent said Friday.
Instead, Don Yee said Wallace (Cordova High, Sacramento City College) met with 49ers coach Jim Harbaugh the morning of the game and said he didn't want to play if it meant mop-up work at the end.
After the game, Harbaugh said Wallace, 33, told him he's retiring.
"That is not my understanding," Yee said. "My understanding is that Seneca will continue his football career but that there was a discussion about his situation, particularly with the 49ers."
When San Francisco signed Wallace on Aug. 22, fellow backup Colt McCoy seemed to be on shaky ground after two poor outings. However, three days later, McCoy showed modest improvement against the Vikings - and, perhaps more importantly, restructured his contract - and Harbaugh named him the No. 2 quarterback. Wallace got in on the last offensive series against Minnesota and completed his only two passes.
Asked Monday about the string of events, Wallace said, "I'm just coming in and trying to do what I can. Harbaugh's been here for a long period of time and has been doing a great job and knows what this team needs. Whatever that is - looking for a No. 2 (quarterback) or a solid No. 3 - I'm just trying to come in and do whatever I can."
Several teams may be looking for quarterbacks after cuts are made Saturday, and it's reasonable to assume that Wallace did not want to risk an injury behind the 49ers' third-string offensive line if he had no chance to make the squad. Wallace expects to be cut Saturday.
Harbaugh said he was surprised by Wallace's decision.
"He felt strongly about it," Harbaugh said. "I don't talk people out of that, you know? I've never seen it done on game day, but I wish him well."
Colin Kaepernick started Thursday's game and was followed by McCoy and rookie B.J. Daniels. That appears to be the team's pecking order at quarterback entering the season.