Chris Culliver, coming off a breakout season in which he played 63.2 percent of the defensive snaps, is widely regarded as the team's most talented cornerback.
It was not out of the question that Culliver, a third-round draft pick in 2011, could have played his way into the 49ers' starting lineup after spending most of his first two NFL seasons as the third cornerback. As the first player first off the sideline when the 49ers employed five defensive backs, Culliver was a big reason the 49ers ranked fourth in the NFL in pass defense during the regular season.
Culliver might have been especially hungry this summer. He declined numerous interview requests through the 49ers' public relations department throughout the offseason and training camp after a disastrous Super Bowl week -- off and on the field. But his play on the field was speaking loudly in the first week of camp.
His quest for an even-larger role in the defense came to a swift, cruel end Thursday morning when he went down with a torn left ACL in a non-contact punt coverage drill. He will be placed on injured reserve when teams are required to make their cuts to 53 players after the final exhibition games.
"There's been some nicks and you try to dodge bullets," 49ers coach Jim Harbaugh said. "Sometimes you don't dodge them all. But what it means right now is there's guys that are getting an opportunity to show what they can do. If there's a positive there. And there's people that are doing that."
So, now, the 49ers have another significant hole to fill in their defensive backfield.
The 49ers lost All-Pro free safety Dashon Goldson, who signed a lucrative deal as a free agent with the Tampa Bay Buccaneers.
Rookie Eric Reid has gotten off to a solid start and appears to be the front-runner to break camp as the starter. Still, it's unlikely the 49ers can get the same kind of production at the position that Goldson supplied.
"Eric's a smart player," 49ers defensive coordinator Vic Fangio said. "He's diligent. The game's not too big for him. He's just going through the normal growing pains of a rookie, learning the system, learning the NFL style of play, the tempo picks up, etc. But he's doing fine."
Culliver's absence will have a great impact on the 49ers, too. After all, Culliver played 63.2 percent of the snaps last season. Culliver allowed a completion percentage of just 49.3 and a 76.9 passer rating when targeted, according to Pro Football Focus.
The 49ers have candidates on the roster to replace him. The club returns its other four cornerbacks from a year ago, and veteran Nnamdi Asomugha has gotten off to a solid start in training camp while playing both sides of the formation.
"He's been good," 49ers coach Jim Harbaugh said of the 10-year veteran. "I think he's got a good grasp of what we're doing defensively. In shape, doing a nice job."
Especially with Culliver's season-ending injury, Carlos Rogers and Tarell Brown appear to have strong grasps on starting jobs they've held together for the past two seasons.
Asomugha appears to be fitting in nicely with the 49ers after two disappointing seasons with the Philadelphia Eagles in which he struggled with the adjustment to the East Coast, as well as a new defense.
"It's a really nice scheme here," Asomugha said. "There's a great mix of man coverages and zone coverages. I don't think they're heavily dominant one way or the other. Maybe a little more zone, as far as the call, but certain things turn into man."
Asomugha could step in for Culliver and play on the outside on the left side while Rogers moves inside to cover the slot receiver.
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But Tramaine Brock and Perrish Cox, the two other returners from a year ago, will also be in the conversation to compete for roles. Last season, Brock was the 49ers' fourth cornerback and Cox was the backup to Rogers in the slot.
When asked if he'd be satisfied with the same role as a year ago, Cox answered, "I won't say satisfied. Wherever I'm needed, I'm going to give it my all. If they need me anywhere, starting, backup, I'm there."
General manager Trent Baalke has not ruled out the possibility of adding six-year veteran cornerback Eric Wright to the mix, too.
The 49ers voided a recent trade for Wright from the Tampa Bay Buccaneers due to a failed physical. The 49ers' medical staff determined Wright was not ready to practice with an undisclosed physical condition, Baalke said. The Buccaneers immediately released Wright, 28, making him a free agent.