Chris Culliver's knee injury looked serious when it occurred around 12:30 p.m. this afternoon. And it is. Both ESPN and NFL.com are reporting that Culliver, the team's No. 3 cornerback the last two years, tore his ACL and will miss the season.
Culliver was dueling with fellow cornerback Marcus Cooper while running down the field to cover a punt. He switched directions and then went down in a heap and immediately clutched at his left knee. It was similar to the motion that tore linebacker Darius Fleming's left ACL on Sunday. Fleming was covering a kickoff and also was going one-on-one against a defender when he switched directions and went down.
Culliver played 63 percent of the 49ers' defensive snaps last year. His replacement in Thursday's session was Tramaine Brock. But several others could win that role, including Nnamdi Asomugha or Perrish Cox. The 49ers also haven't ruled out signing Eric Wright, whom they traded for last month but who failed a physical with the team.
Asomugha in particular has played well in recent practices, and he got praise from Jim Harbaugh on Thursday. "Yeah, he did have noticeable, eye-popping plays, yesterday especially," Harbaugh said. "He's been good. I think he's got a good grasp of what we're doing defensively. In shape, doing a nice job.
Culliver is one of the few cornerbacks under contract for next season. Tarell Brown, Asomugha, Brock and Cox all are entering the final year of their deals. (Cox is a restricted free agent). Another cornerback, Carlos Rogers, will count a team-high $8.1 million against the salary cap next season.
-- Matt Barrows