An MRI confirmed Minnesota's worst fears - 26 win over the Washington Redskins.
Peterson, who was playing in just his second game after missing the previous three with a high ankle sprain, was helped off the field after taking a helmet to the knee from Redskins safety DeJon Gomes on a run up the middle early in the third quarter.
Peterson had rushed for 38 yards and a touchdown before leaving the game.
Head coach Leslie Frazier will give a further update Monday at his press conference.
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