MINNEAPOLIS - Vikings head coach Mike Zimmer confirmed what many suspected, that rookie running back sensation suffered a torn ACL in Sunday's game against Detroit.

Cook's left knee buckled early in the second half while he tried to plant it and make a cut toward the end of a run, and Lions safety Tavon Wilson popped the ball out with his tackle.

Cook limped off the field with help from head athletic trainer Eric Sugarman. Zimmer told reporters Monday that the rookie, who has been an integral part off the Vikings offense in the first four games, tore his anterior cruciate ligament and will undergo reconstructive surgery as soon as the swelling goes down.

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While Zimmer did not say Cook is done for the season, the average recovery time for a torn ACL is 12 months.

Cook has 354 yards rushing in four games, good for second in the league. The versatile Latavius Murray, who signed in the off-season as a free agent from Oakland, is expected to carry the load the rest of the season, although Zimmer did not rule out signing another running back.