The Minnesota Vikings couldn’t have scripted a better start to “Sunday Night Football” against the Seattle Seahawks in Week 5, but now the key to their offensive success could be sidelined moving forward. After racking up nearly 90 yards from scrimmage in just over two quarters to start Sunday’s matchup, star running back Dalvin Cook suffered a groin injury on a third-quarter catch and is set to undergo an MRI for the ailment on Monday.

The injury initially forced Cook to leave Sunday’s game and undergo a locker-room evaluation, thrusting backup Alexander Mattison into the No. 1 running back spot for the Vikings, who deemed Cook questionable to return. The Pro Bowler did, in fact, return to the sideline — and then onto the field — later in the third quarter, but not for long. Mattison quickly resumed the full workload at running back, with Cook retreating to the sidelines after just one more play. Coach Mike Zimmer said afterward Cook couldn’t play through the injury.

A 1,000-yard breakout rusher in 2019, Cook entered Sunday night’s affair as the NFL‘s leading ball-carrier through four weeks, with 424 yards and six touchdowns to his name. Fresh off a five-year, $63 million contract extension inked in September, he’s been the centerpiece of Minnesota’s offense for the last two years, scoring a career-high 13 touchdowns in 2019.

Injuries, however, are no stranger to the 25-year-old back. Cook missed 19 combined games between 2017 and 2019, including 12 as a rookie and five in his sophomore season. If he ends up missing more time in the Vikings’ backfield, the team would figure to rely on Mattison, their 22-year-old former third-rounder, as well as reserve Mike Boone and veteran fullback C.J. Ham.