Cook will undergo season-ending surgery to repair the torn ACL in his left knee, Vikings coach Mike Zimmer confirmed Monday.
The rookie running back, who was on pace to top 400 yards rushing through the first four games of the season, suffered a noncontact knee injury early in the third quarter Sunday.
Cook took a handoff from Case Keenum up the middle of the field for a 10-yard gain. Upon cutting to his right to avoid being tackled by Lions safety Tavon Wilson, Cook reached down to grab his left knee and fumbled the ball.
Zimmer said Cook will need to wait until the swelling goes down before having surgery. The likelihood of the knee having sustained other damage didn't raise any red flags.
"Like on most of these ACLs, there's a little bit of cartilage, meniscus," Zimmer said. "It's a normal, typical ACL (tear)."
Zimmer spoke with Cook on Sunday about the confidence that he has in the Vikings' medical staff to help the running back return after surgery.
Minnesota has dealt with an onslaught of noncontact knee injuries within the past 13 months with quarterbacks Sam Bradford and Teddy Bridgewater, and before that with former running back Adrian Peterson, who returned from an ACL tear that he sustained at the end of the 2011 season and was named the NFL's MVP during his 2012 campaign.
"I talked to him last night about it," Zimmer said. "About the doctors that we have here and the medical staff and how they were able to rehab the last great runner here. I expect (Cook) to come back and be the same as he was."
With Cook sidelined for the rest of the season, Minnesota will look to Latavius Murray to take on the rookie's workload.
Murray signed a three-year, $15 million contract in the offseason before undergoing ankle surgery that kept him out for several months. Zimmer did not rule out the possibility of the Vikings signing another running back to help out in Cook's absence.
"Maybe, yeah," Zimmer said. "We're looking at everything now."
Murray rushed for 788 yards and 12 touchdowns last season with the Oakland Raiders. The veteran missed a bulk of the preseason while recovering from his surgery and was limited in his role through the first four weeks as Cook's success continued to crescendo.
Though he says his ankle is not at health just yet, Murray feels that he's able to take on an increased workload (Cook averaged 18.5 carries in four games) should the Vikings need him to do so next Monday in Chicago and going forward.
"To be honest, I think I'm still getting to that point," Murray said of his ankle getting back to 100 percent. "I think it's not going to quite feel the same for awhile. I knew that dealing with my previous ankle procedure.
"For me it's being well enough to be out there and being able to help the team and be successful. I guess I don't know when that day will come. I didn't remember when that day came (previously). I know I was just like 'I really don't feel it anymore.' I feel good enough to be out there and I'm confident in myself that I can play at a high level."
Murray, who rushed seven times for 21 yards after Cook went down Sunday, said his ankle is the furthest thing from his mind during a game. The most he said he's dealt with postgame has been "general soreness."
"I think you rarely find somebody that's feeling 100 percent from Week 1 through the rest of the season," he said. "I feel good enough, I feel great, actually, to be able to handle any workload."
"Any time you have surgery on something you're never going to be 100 percent," Zimmer added. "But he said he's ready to go and we're ready to have him."