Vikings running back Dalvin Cook dislocated his left shoulder on a third-quarter fumble during Sunday's loss to the 49ers, and he could miss some time following the results of a MRI on Monday morning.

Cook tore the labrum in his left shoulder, as first reported by NFL Network. A source familiar with the injury said a labral tear almost always accompanies a dislocated shoulder, meaning the result of Cook's MRI was widely expected, but the injury continues the running back's history of shoulder issues dating back to college.

He had surgery on his right shoulder at Florida State in 2016, and missed the final two games of the 2019 regular season after tearing the labrum in his right shoulder. The Vikings chose to sit Cook and get him ready for the playoffs, and he returned with 130 yards from scrimmage in their wild-card victory over the Saints.

Coach Mike Zimmer would not confirm details about Cook's injury, saying the running back was day-to-day. "That's what they're telling me," he said.

The Vikings play on Sunday in Detroit, and return home for a Thursday game against the Steelers four days later. Given the timing of Cook's injury, he could miss both games before the Vikings travel to Chicago for a Monday night game on Dec. 20.

"I know Dalvin is going to bounce back," wide receiver Justin Jefferson said after Sunday's game. "We don't know how serious that injury is, but just keeping him in our prayers and hopefully he's OK and comes back for us."

Cook had missed two games earlier this season with an ankle injury: Week 3 vs. Seattle and Week 5 vs. Detroit, both Vikings victories. Cook is averaging 85.9 rushing yards per game after posting 111.2 last season.

Alexander Mattison figures to start in Cook's absence, though the Vikings could also involve rookie Kene Nwangwu, who returned his second kickoff of the season for a touchdown on Sunday and got his first work in the Vikings' offense, with a 7-yard carry after Cook was carted off in the third quarter.

"He's still learning some of the run game," Zimmer said. "They call it where the dot is, and then trying to get to stretch that dot and bring it back the other way or continue to go to the perimeter. Just continue learning. He's doing a good job."

Mattison started against Seattle and Detroit with Cook out earlier this season and ran for 112 and 113 yards, respectively.

"He's done a nice job when he's been in there," Zimmer said. "We anticipate him, if he has to play, going in there and playing well."