SANTA CLARA, Calif. (AP) – San Francisco cornerback Walt Harris could miss the upcoming season after tearing a ligament in his right knee, dealing an early blow to the 49ers’ hopes of a return to playoff contention.

Harris, a 13-year pro entering his fourth year with the 49ers, was injured during Tuesday’s practice in a collision with receiver Dominique Zeigler. Although Harris had to be helped off the field to sit on a cart, the team initially thought the injury wasn’t major before tests revealed the serious problem.

The 34-year-old Harris will need surgery on his anterior cruciate ligament, which is at least partially torn. Such operations typically require several months of rehabilitation.

Harris has been a model of consistency in his lengthy career, never missing more than four games in a season. Harris’ consistent veteran presence was expected to be a cornerstone of coach Mike Singletary’s defense, particularly given the shallow depth behind him.

Tarell Brown probably will take Harris’ place atop the 49ers’ depth chart opposite fellow cornerback Nate Clements. Brown, a Texas product who slipped to the fifth round of the draft two years ago, is eager to step in.

“I’m coming into my third year, and I know the scheme like the back of my hand,” Brown said. “I feel like I’m one of the most athletic players on the football field every time I step onto the field. … I always see myself as a starter. I’m going to work every day like I’m a starter.”

Shawntae Spencer, a longtime starter at cornerback for San Francisco, still hasn’t returned to practice after missing 14 games last season with a knee ligament injury. The 49ers waived defensive back Jimmy Williams earlier in the week, further depleting their depth.

Harris, who has 35 career interceptions and four touchdowns, also played for Chicago, Indianapolis and Washington. He was chosen for the Pro Bowl during his first season with San Francisco in 2006, when he had eight interceptions.

The 49ers lost Zeigler to a concussion later in Tuesday’s practice after a collision with safety Dashon Goldson. Zeigler isn’t expected to participate in Thursday’s workouts, but might return next week.

Receivers Arnaz Battle and Jason Hill also have sat out workouts with minor injuries. Defensive lineman Kentwan Balmer also sprained his knee during Tuesday’s drills, but the injury isn’t thought to be serious.

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