Safety Tony Jefferson, one of the Ravens' defensive leaders and leading tacklers, suffered a season-ending knee injury in Pittsburgh.
"He at least has an ACL, probably more," Head Coach John Harbaugh said. "So he'll be out for the season, as it stands right now."
The team circled around Jefferson in the postgame locker room for a prayer.
"All things are possible," Harbaugh said. "And he'll find a way to come back stronger than before."
Jefferson's injury happened in the fourth quarter on a long pass intended for tight end Nick Vannett. Jefferson went down and seemingly grabbed Vannett as he fell to the turf to prevent the tight end from breaking wide open.
The pass was intercepted by safety Earl Thomas, so the penalty wiped out the turnover. But the Ravens were immediately more concerned with Jefferson's status than any penalty. Several teammates knelt next to Jefferson in prayer on the field as he immediately grabbed his knee.
Jefferson went off the field without putting any weight on his left leg and was taken straight to the locker room on a cart. He was immediately ruled doubtful to return.
Third-year safety Chuck Clark replaced Jefferson in the game and finished with two tackles, including one for loss. The Ravens could also turn to second-year safety DeShon Elliott as they move forward.
Jefferson was wearing the Ravens' helmet with communication for the second straight game, a job he took over from inside linebacker Patrick Onwuasor.
Jefferson is one of the Ravens defense's most important and beloved players, both from an on-field perspective and in the locker room.