The San Francisco 49ers waited until Week 10 of the season to get Christian McCaffrey back. Now it appears his campaign is over after just four games.

Speaking in his postgame press conference after the 49ers' latest loss, a 35-10 defeat to the Buffalo Bills, head coach Kyle Shanahan said they believe McCaffrey suffered a PCL injury to his right knee in the second quarter that will likely end his season.

McCaffrey was enjoying his most explosive performance since returning from bilateral Achilles tendinitis last month, but left the game after sliding down for a five-yard loss on a run to the outside on which he was clearly hobbled.

But it appeared McCaffrey sustained the injury on his previous carry, an 18-yard surge that looked like he could have taken the distance, only for a shoestring tackle by Taylor Rapp to bring him down, with the running back landing hard on his knee.

McCaffrey's strong start to the game, which saw him rack up 67 yards from scrimmage before he left, followed a week in which he practiced in full on a Thursday for the first time since returning.

The big plays he was able to make reflected an apparent improvement in his physical state, heightening the disappointment of losing him to another injury for San Francisco.

"It was frustrating," Shanahan told reporters. 

"He had a great week of practice. I thought he came out great. Hurt for him and tough for our team not having him."

Now the 49ers will likely have to get used to not having McCaffrey again, the reigning Offensive Player of the Year seen leaving the locker room on crutches and in a knee brace, per Jennifer Lee Chan of NBC Sports Bay Area.

So the Niners will now turn back to Jordan Mason and rookie Isaac Guerendo on the ground as they look to somehow salvage their season after dropping to 5-7.

With Mason going for 78 yards and Guerendo scoring the 49ers' only touchdown against Buffalo, the rushing attack will still be in capable hands.

But in a season defined by missed opportunities, it will sting especially hard that McCaffrey's season seemingly came to an end on a play where he looked to primed to announce himself as being back to his devastating best.

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