SANTA CLARA -- Kyle Williams, the 49ers' top kick returner, won't be coming back.
Williams announced via Twitter on Monday that his season is over in the wake of a left knee injury sustained Sunday against the New Orleans Saints.
"Regret to inform y'all I will be out for the season with a torn ACL,'' he wrote. "Not how I saw things playing out, but in the end I will be fine.
"This is just another obstacle. I will have to climb back."
Coach Jim Harbaugh had declined an hour earlier to discuss specific injuries, but hinted that Williams and running back Kendall Hunter (ankle) had serious issues.
When asked if a pair of dormant top draft picks, receiver A.J. Jenkins and running back LaMichael James, might be needed on the field this week, Harbaugh said: "There's a good chance there'll be some new active guys."
Williams, 24, led the 49ers this season with a 27.2-yard average on his 13 kickoff returns. He also had four punt returns and a 13.0-yard average.
The San Jose native also had 14 catches for 212 yards as a receiver.
Harbaugh said that Hunter was still being evaluated. There was also no medical update on tight end Delanie Walker, who left Sunday's game with a hip injury.