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When Latavius Murray signed a three-year, $15 million deal with the Vikings in March, he effectively ended the Adrian Peterson era in Minnesota. A month later, when rookie Dalvin Cook slid to the Vikings in the second round of the NFL draft, Murray became an expensive insurance policy.

Now the Vikings need to cash in on Murray.

"I never want to be out there at the expense of somebody being injured," Murray said after the Vikings' 14-7 loss to the Detroit Lions on Sunday at U.S. Bank Stadium. "I'm disappointed and feel for [Cook]."

Cook went down on his 13th carry Sunday, dropping the ball and clutching his left knee immediately after planting it into the artificial turf. The Vikings fear Cook tore his anterior cruciate ligament, according to coach Mike Zimmer, which would end the dynamic rookie's season before it really got going. Cook will have a magnetic resonance imaging exam Monday.

Zimmer admitted the Vikings will need to tweak the offensive approach without Cook, whose hot start — he is averaging nearly 5 yards per carry — stated his case for NFL Rookie of the Year. Cook amassed 444 yards from scrimmage before going down.

"Dalvin's a really explosive player," Zimmer said. "He has such great big-play ability. We'll have to look at things differently. If you lose a guy like him, you lose a lot of firepower."

From the start, the Vikings envisioned this 2017 offense as flowing through their running backs. An effective passing game through the first three weeks relied on Cook and the rushing attack to set up play-action passes.

So enter Murray, the fifth-year pro and 2015 Pro Bowl selection largely left out of game plans behind Cook. Murray had only seven carries on 17 snaps in the Vikings' first three games. He stepped in Sunday and finished with 21 rushing yards on seven runs.

"It's not about whether or not I'm ready or what rhythm I have," Murray said. "I need to be ready when my number is called."

Jerick McKinnon, the Vikings' No. 2 back previously, will also be a factor. But he struggled against Detroit before suffering an ankle injury. He declined to comment after the game.

The Vikings signed Murray after watching him be an effective every-down threat with Oakland for three seasons. Murray ran for a career-high 1,066 rushing yards in 2015 and last year compiled 12 rushing touchdowns for the Raiders.

The Vikings will miss Cook's slashing runs and elusive accelerations. Murray, who had offseason ankle surgery that kept him out for much of this preseason, likely surrenders a step to the rookie. In ony four NFL games, Cook popped off a 20-yard run five times. Murray had five 20-yard runs all of last season.

But Murray, who is regarded as a solid all-around back, said he hopes the Vikings don't need to change much in Cook's absence.

"I have all the confidence in myself, and I believe the coaches have the confidence in me," Murray said, "that I could catch the ball, run the ball, block and let the offense do all the things we've been doing."