After a 27-13 victory against the Tampa Bay Buccaneers, Niners coach Kyle Shanahan said Hufanga had "most likely" torn the ligament but further testing would be needed to confirm that. Hufanga had those tests Monday morning and the Niners' fears were confirmed, though the imaging showed no additional damage in the knee.
"He does have a torn ACL," Shanahan said. "They don't think there was any meniscus or anything, so it's as clean as it could be."
Hufanga, who was a first-team All-Pro in 2022, suffered the injury on a pass play with 8:40 left in the third quarter. On the play, Bucs quarterback Baker Mayfield dumped a pass off in the right flat to running back Rachaad White.
As White worked upfield, Hufanga closed in to attempt the tackle but bit on an inside fake from White, who ran past him for an 11-yard gain. Hufanga planted his right leg into the ground and when he attempted to turn with White's cut, the knee appeared to buckle.
Hufanga was slow to get up after the play and went straight to the blue medical tent on the sideline. After spending a few minutes in the tent, a cart came out and took Hufanga to the locker room. He was ruled out almost immediately, a sign that the Niners believed the injury to be serious.
Through 10 games, Hufanga is fourth on the team in tackles (51) and tied for first in interceptions (3).
"I thought he started out well," Shanahan said. "I thought he hit a little lull during our skid and I thought he played one of his best games versus Jacksonville, and I thought the same thing was going to happen here, but I thought he was going to end up having a real good year."
In his third season, Hufanga will be eligible for a contract extension for the first time in the offseason. His injury makes that situation a bit murkier, but Shanahan indicated that Hufanga should be ready to go at the start of next season.
"He will need a plan for training camp, but with the time and everything, if everything goes smoothly, he should be ready for Week 1," Shanahan said.
The Niners turned to rookie safety Ji'Ayir Brown to replace Hufanga on Sunday and will continue to do so moving forward. Brown, who has mostly contributed on special teams, had a couple of rough moments soon after entering but settled in and finished with four tackles, three passes defended and his first career interception to seal the win against the Bucs.
Brown has made a good impression in San Francisco's locker room since arriving as a third-round pick, and teammates such as linebacker Fred Warner believe he's ready to step in.
"My heart goes out to Huf," Warner said on Sunday. "That is sickening news. To talk about the way Ji'Ayir played today and being ready for his moment, can't say enough about it, that's huge."
For his part, Brown said he has been doing all he can to learn from the veterans in case his opportunity arrived. Now that it has and he has valuable experience from Sunday under his belt, Brown said he feels good about his ability to help the defense.
"I'm always confident," Brown said. "When you got guys around you that's Pro Bowlers, that's just great players, you want to live up to their standard when you go out there. I like to play for those guys on the field, show 'em that I belong out there with them."