Coach Mike Zimmer did not have an update on Cook's condition following the Vikings' 34-26 loss to the 49ers but said the running back would undergo an MRI on Monday.
Cook was injured after being brought down by Niners defensive tackle Kevin Givens following a handoff. The running back lost the ball in the process of being tackled and immediately grabbed for his chest with his right arm when he hit the ground.
He remained down on the field for several minutes as athletic trainers tended to him. Both Vikings and Niners players knelt around Cook while he was being moved onto a cart before being taken off the field and back into the locker room for further evaluation.
Cook's day ended with 10 carries for 39 yards and six receptions for 64 yards. He was replaced by backup running back Alexander Mattison, who rushed three times for 8 yards and caught one pass for 2 yards after Cook left.
While Zimmer did not comment on Cook's status postgame, the coach hinted at the running back having to miss time when asked about rookie running back Kene Nwangwu, who returned a kickoff 99 yards for a touchdown in the third quarter. Nwangwu has been used solely on special teams but could find his way into the game plan on offense going forward.
"I think there's a chance he might end up getting some more playing time," Zimmer said of Nwangwu.