The reigning league MVP, Peterson later walked under his own power while moving from the Vikings' locker room to the X-ray room.
He did not return to the game.
Coach Leslie Frazier said after the Vikings' 29-26 loss that the team's initial diagnosis was a sprained foot. Peterson said he would undergo an MRI on Monday.
Peterson immediately rolled over in pain and had to be helped off the field. He was taken to the locker room in a cart after doctors examined his leg on the sideline.
Peterson, who was questionable to play in Sunday's game because of a groin injury, had carried a combined 67 times in the Vikings' previous two games and had vowed to play. Peterson had gained just 13 yards on seven carries, as he was unable to find much running room on a snowy field in Baltimore.
If the injury is serious, it would be the second one for Peterson in the state of Maryland in less than two years. He tore his left ACL on Christmas Eve in 2011, in a game against the Washington Redskins at FedEx Field in Landover, Md.