Pittsburgh lost more than a game on Sunday evening.
Conner had 74 total yards and two rushing touchdowns on 18 touches at the time of his departure. The back was replaced on the drive by Jaylen Samuels, who tied the game on a catch-and-run touchdown.
There was little information on the severity of Conner's injury after the game. He was seen by local reporters walking around the locker room without a noticeable limp following the loss.
"I hate to even comment without knowing what's going with James or anything," quarterback Ben Roethlisberger added, "so we'll proceed as we need to moving forward."
Conner has suffered multiple MCL injuries in the past and spent time in concussion protocol a few weeks ago, but had not been seriously bit by the injury bug this season until Sunday evening. The setback interrupts what has been a magical season for Conner. In taking over the starting role from Le'Veon Bell, Conner entered Week 13 third in the league in rushing and rushing touchdowns.
Pittsburgh shouldn't have a hard time without Conner next week, when it travels to Oakland, but if the running back is out for an extended period of time, the Steelers are at risk of losing a major facet of their offense and their lead in the AFC North.