San Francisco 49ers star Christian McCaffrey sat out Sunday night’s 35-10 loss to the Buffalo Bills with a knee injury, but it appeared to be much worse.

McCaffrey is believed to have suffered a posterior cruciate ligament (PCL) injury and his season could “potentially” come to an end, 49ers head coach Kyle Shanahan said.

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San Francisco 49ers running back Christian McCaffrey, #23, tackles Buffalo Bills safety Taylor Rapp during the first half of an NFL football game in Orchard Park, New York, on Sunday, December 1, 2024. Tail light, on. (AP Photo/Adrian Kraus)

“I think PCL usually lasts a few weeks, but I’m not sure yet,” he added.

The running back was a key part of the 49ers’ game plan early on against the Bills. As snow fell on the field at Highmark Stadium, McCaffrey ran the ball seven times and was targeted three times through the air.

He had 53 rushing yards and two catches for 14 yards before leaving the field.

It was a huge blow for a team plagued with injuries on both sides of the ball. The snow made things even worse for San Francisco. Brock Purdy had just 94 yards on 18 attempts.

“He’s one of the best running backs in the league,” Purdy said of McCaffrey. “When you lose him like that, I think it loses some things offensively.”

San Francisco 49ers running back Christian McCaffrey, #23, is hit by Buffalo Bills safety Damar Hamlin, #3, during the first half of an NFL football game in Orchard Park, New York, on Sunday, December 1, 2024. (AP Photo/Adrian Kraus)

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Shanahan said he believed McCaffrey was injured after he was tackled following an 18-yard run in the second quarter. He went down a few games later.

“It looked like he was just sweating it out there and was about to cancel a house call,” Shanahan said. “It was frustrating. He had a great week of training. I could feel his urgency and stuff. I thought he did great and looked really good.”

McCaffrey was on the shelf for most of the season. The reigning Offensive Player of the Year missed the first eight games of the season due to Achilles tendonitis.

San Francisco 49ers running back Christian McCaffrey speaks to the media after NFL football practice in Santa Clara, Calif., Tuesday, June 4, 2024. (AP Photo/Tony Avelar, File)

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In the four games he played, he had 202 rushing yards and 15 catches for 146 yards. He hasn’t scored a goal this season.

The Associated Press contributed to this report.

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