Running back James Conner, who entered Sunday's game leading the AFC in rushing, left in the fourth quarter of the Steelers' 33-30 last-second loss and did not return.
Conner, who earlier scored a pair of touchdowns to give him 12 on the season, caught a short pass over the middle from Ben Roethlisberger and took it upfield for a 10-yard gain to the Chargers' 16 with 4:45 remaining.
But as he was being tackled, Conner's leg was caught under safety Adrian Philips. Conner initially got up off the ground but then went back down and was attended by trainers before being helped from the field.
He briefly went under the observation tent and then went to the locker room for X-rays. Results of those were not made available, but Mike Tomlin called the injury a "contusion."
Roethlisberger didn't want to speculate on the severity of the injury.
"I hate to even comment on anything without knowing what's going on with James," Roethlisberger said. "We will proceed as we need moving forward. I just don't know how to answer."
Conner has taken over as the Steelers' lead running back in his second season after Le'Veon Bell refused to report and sign his franchise tender with the team. At the time of his injury, Conner had 15 carries for 60 yards and two touchdowns and had caught three passes for 14 yards.
