San Francisco running back Christian McCaffrey suffered a knee injury that coach Kyle Shanahan described as “potentially” season-ending in the 49ers’ 35-10 loss to the Buffalo Bills on Sunday night. Shanahan said McCaffrey is believed to have injured his posterior cruciate ligament, which connects the thigh bone to the shin. He said he had no timetable for McCaffrey’s return but acknowledged the All-Pro’s season could be over. It’s the latest setback in a frustrating season for the 2023 offensive player of the year, who missed the Niners’ first eight games with Achilles tendinitis and has not been his usual explosive self since returning.