SANTA CLARA Kyle Williams, the 49ers' valuable return man, is done for the season.
The wide receiver tweeted Monday that he sustained a season-ending left knee injury in Sunday's 31-21 victory over New Orleans.
"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."
Williams crumpled to the ground after a two-yard run by Kendall Hunter near the end of the third quarter. On the same play, Hunter suffered a potentially serious ankle injury.
Coach Jim Harbaugh declined to discuss specific injuries Monday, saying players were still being evaluated. But he acknowledged the 49ers' top two draft picks might finally hit the field.
Wide receiver A.J. Jenkins (first-round pick) and running back LaMichael James (second round) have yet to play this season.
Asked about the outlook for Jenkins and James, Harbaugh said, "There's a good chance there'll be some new active guys on Sunday (at St. Louis). To both those youngsters' credit, and others who have been working extremely hard for their opportunity, we feel good and excited that a couple of those youngsters will get that opportunity."
Williams led the 49ers this season with a 27.2-yard average on his 13 kickoff returns. As the No. 3 wide receiver, he had 14 catches for 212 yards.
With Williams poised to go on injured reserve, the 49ers could sign another player. Former Philadelphia wide receiver-returner Chad Hall is a possibility, according to Adam Caplan, an analyst for philadelphiaeagles.com.
Kaplan reported the 49ers have interest in Hall, who later tweeted, "California, California, hear we cooooooome."
Et cetera There was no update on tight end Delanie Walker, who left Sunday's game because of a hip injury. "We'll see," Harbaugh said. "We haven't got the final report. It was a hard-hitting game. It took a toll."
Among the things that most pleased Harbaugh about his team's defensive effort Sunday was its sure tackling. He suspected there was only one missed tackle but wanted to watch the game film to make sure.