Injury updates: Percy Harvin, Chris Culliver

SANTA CLARA, Calif. -- Another day, another potentially significant injury to consider.

San Francisco 49ers cornerback Chris Culliver was running downfield during practice Thursday when he fell to the ground and clutched his knee. The 49ers scheduled an MRI exam. They did not yet know the extent of the damage. They did not speculate.

Culliver was covering a punt during a non-contact portion of practice. There was no collision of significance. Culliver initially sat on the ground and extended his left leg a couple times. Medical personnel arrived. Culliver lay down onto his back while the medical staff inspected his knee. Culliver increasingly appeared to be in pain. Medical people helped him up. Culliver put very little weight on his left leg while medical personnel helped him off the field to a cart positioned along the sideline. Culliver sat in the passenger seat of the cart and was taken across another field toward the locker room.

Culliver has been the 49ers' third cornerback. He generally defends outside receivers in the nickel package, with starter Carlos Rogers shifting inside to defend the slot. San Francisco already has depth concerns at corner. The team acquired cornerback Eric Wright from Tampa Bay, only to nix the deal when Wright failed a physical exam. Veteran Nnamdi Asomugha's value to the team figures to increase if Culliver is lost for an extended period, although Tramaine Brock was the next man up once Culliver departed.

At least the 49ers' secondary won't have to worry about facing the Seattle Seahawks' Percy Harvin in Week 2. They might get a shot at him when the teams play a rematch in Week 14.

Harvin underwent hip surgery as expected Thursday. Coach Pete Carroll told reporters there's a chance the receiver could return late in the season. Seattle will presumably leave Harvin on its active/physically unable to perform (PUP) list. Harvin would then land on the reserve/PUP list when teams cut down to 53 players Aug. 31. Harvin would stop counting against the active roster at that time. He would be able to return as early as Week 7 or as late as Week 15 under PUP rules. The Seahawks visit the 49ers on Dec. 8, in Week 14.

"What we have heard so far is that the surgery went very well, and that there’s a long rehab process coming up," Carroll said. "He's going to be in New York for a couple of weeks to start off the rehab, and we'll get him back here in due time. We don't have any dates or timelines, but we're going to be very optimistic and hope that he gets back as soon as possible, and we're glad that we got him fixed up and he’ll be ready to go."

Carroll said he thinks Harvin has "a chance" to return at some point this season.