Vikings running back Dalvin Cook exited early in the third quarter of Sunday's 27-26 loss to the Seattle Seahawks after pulling up during a run and grabbing his left groin.
He tried to shake it off, returning for one snap before ceding his workload to Alexander Mattison.
Coach Mike Zimmer said Cook will undergo an MRI on Monday. Cook immediately went to the locker room after pulling up on his 22nd touch of the night, a swing pass to the flat. He started hobbling before reaching the sideline, where he was knocked out of bounds by Seahawks safety Ryan Neal.
Cook returned for one play, an interception by quarterback Kirk Cousins.
The injury marked a momentum shift. The Vikings punted, and Seahawks quarterback Russell Wilson threw a 19-yard touchdown pass on the next drive. Seattle took a 14-13 lead before Cook's brief return, and Seahawks running back Chris Carson scored to make it 21-13 after the interception.
"Obviously, you don't want to lose a guy like Dalvin," receiver Adam Thielen said. "He's such a dynamic football player and means so much to this offense."
The Vikings had to find a way without Cook, the NFL's leading rusher entering Week 5. He was again the offense's centerpiece, compiling 21 touches by halftime, and had 65 rushing yards and 24 receiving yards before exiting.
While the Vikings built a 13-0 lead, Cook and Mattison combined for 128 of 217 first-half yards.