The Vikings confirmed that Cook (knee) has a torn ACL, Courtney Cronin of ESPN.com reports.
The 41st overall pick in this year's draft, Cook was well on his way to a huge rookie season before he injured his knee in the second half of Sunday's 14-7 loss to the Lions. He piled up 74 carries for 354 yards (4.8 average) and two touchdowns in four games, adding 11 receptions for 90 yards on 16 targets. Cook's absence leaves Latavius Murray and Jerick McKinnon (ankle) to handle backfield work, with Murray the best bet to serve as the Vikings' lead runner. Murray has struggled to make his way back from offseason ankle surgery and admitted Monday that he still isn't quite at his best. McKinnon left Sunday's game in the fourth quarter with an ankle injury of his own. The Vikings may become highly dependent on their passing game once Sam Bradford (knee) returns. Cook suffered his injury early enough in the season that he'll at least have a shot to make it back for the start of training camp next year.