An MRI revealed that Vikings running back Adrian Peterson tore the ACL in his left knee during Saturday's 33-26 win over the Redskins. A source with knowledge of the situation told ESPN's Josina Anderson that the MRI also revealed that Peterson tore the MCL in his knee. Peterson said earlier Saturday that he knew "it was something bad" the moment he was hit and that he was in "severe pain" as he lay on the field. He was hurt when tackled by Redskins safety DeJon Gomes at the end of a 3-yard gain on the first offensive play of the second half. "Anytime you take a blow to the knee like that, you're concerned about the ACL, MCL," Peterson said as he stood on crutches in the locker room. "I'm trying to stay as positive as I can."