The Vikings star running back was ruled out after taking a hard hit from Niners defensive tackle Kevin Givens late in the third quarter. Cook laid on the ground in pain for several minutes before eventually getting carted off the field after being tended to by trainers.
Vikings coach Mike Zimmer said after the game that he's unsure of the extent of Cook's injury but more will be known once he undergoes an MRI.
NFL Network Insider Ian Rapoport reported that Cook suffered a dislocation and the upcoming tests are to determine what damage the dislocation caused.
In addition to the loss of one of their best players, the sequence proved costly for Minnesota in more ways than one as San Francisco seized momentum with a fumble recovery after Cook coughed up the ball on the play.
The Vikings trailed 31-26 at the time of Cook's exit, and that deficit would increase after the Niners capitalized on the favorable field position with a Robbie Gould field goal four plays later. The Vikings would get two more chances to tie the game but came up empty.
Alexander Mattison again proved his value as a capable backup but it's no secret Minnesota's final drives would've been bolstered by Cook's presence. Mattison finished the game with seven carries for 21 yards and a score, which came early in the third following a big Cook reception.
Ranked sixth in rushing yards entering Week 12, Cook was in the midst of quiet afternoon on the ground before getting injured, rushing 10 times for 39 yards. He did, however, make up for that through the air with six catches for 64 yards.
Should the results of the RB1's pending MRI mean more missed time, Mattison's role would increase exponentially in a pivotal Week 13 road clash with Detroit.