Christian McCaffrey followed a troubling gaffe with a troubling exit to the locker room on a snowy night in Buffalo.

McCaffrey slipped on a non-contact run and was forced out of the San Francisco 49ers’ game against the Bills on Sunday night with a knee injury.

McCaffrey, playing in his fourth game of the season after missing the first eight games with Achilles tendon and calf injuries, took a pitch to right and slid to the ground after a step or two. He emerged and jogged to the sidelines, briefly visiting the medical tent before continuing on to the locker room.

In a season where injuries plagued San Francisco, McCaffrey’s was the biggest and first to plague the 49ers. Its new edition is a cause for great concern.

McCaffrey missed training camp and preseason as a precautionary measure because of what was initially described as a calf problem. But McCaffrey’s injury continued and he was placed on injured reserve after Week 1.

McCaffrey didn’t look quite like himself upon returning from IR, averaging just 49.7 rushing yards per game in his first three contests.

After a 5-yard loss on his final attempt Sunday night, he had seven carries for 53 yards and a gain of 19 yards, showing flashes of the old CMC before the injury surfaced.