SANTA CLARA -- The pain and tears that washed over cornerback Chris Culliver's face Thursday were different from that of his miserable Super Bowl week in New Orleans. And it signified a growing list of physical challenges for a 49ers team striving to return to the title game.
Culliver sustained a left-knee injury -- a torn anterior cruciate ligament, according to a league source -- a day after All-Pro linebacker Patrick Willis fractured his right hand. It's been a growing theme for the 49ers since leading receiver Michael Crabtree tore his right Achilles on May 21.
"There've been some nicks, and we try to dodge bullets," coach Jim Harbaugh said. "Sometimes you don't dodge them all. What it means now is guys are getting an opportunity to show what they can do."
While Willis likely will return in time for the season opener from what was termed a "slight fracture" -- the third time in seven seasons he's broken the right hand -- Culliver's third season is done before it starts. An MRI at Stanford Hospital revealed a torn ACL, and he will be placed on the injured-reserve list, a league source confirmed.
Culliver appeared distraught as he climbed onto a cart that took him to the locker room, and general manager Trent Baalke consoled Culliver at one point.
"We wish him the best of luck," said Perrish Cox, who was the punt returner when Culliver got hurt making a seemingly routine cut as the coverage team's gunner.
Culliver was the team's nickel back last season, playing behind starters Tarell Brown and Carlos Rogers. Culliver also left Wednesday's practice early, because of an apparent upper-body injury.
Culliver was unavailable for comment, and he hasn't granted any interview requests this training camp. He drew scorn during Super Bowl week for homophobic comments, and he later struggled in the 49ers' 34-31 loss to the Baltimore Ravens.
After Culliver's injury Thursday, Tramaine Brock moved up to the first-string defense and played left cornerback when Rogers shifted into the slot, with Brown at right cornerback.
"He's quick, aggressive, a tough player, feisty," Harbaugh said of Brock, who has two interceptions in 30 career games.
Nnamdi Asomugha remained the second-string right cornerback and put together another impressive practice, including a goal-line pass defense of a Scott Tolzien throw toward Chad Hall.
"He did have some eye-popping plays, especially yesterday," Harbaugh said of Asomugha. "He has good grasp on the defense, he's in shape and doing a nice job."
Collie, 27, worked out for the 49ers on June 13 but wasn't offered a contract. He and Robinson, 28, recently worked out for the Miami Dolphins at the same time.
Robinson, 28, caught 24 passes in seven games for the Jaguars last season. He is a six-year veteran. Collie, 27, caught one pass in the only game he played last season, his fourth with the Colts.
Collie averaged 57 receptions and totaled 16 touchdowns his first three seasons with the Colts. Concussions derailed his once-promising career.
Moody and Wilhoite later combined on an interception, with Moody tipping a Kaepernick pass that Wilhoite grabbed.