Minnesota Vikings running back Dalvin Cook has an adductor strain, a source told ESPN's Adam Schefter.
Cook was injured on the first play of Minnesota's opening drive in the second half of Sunday night's loss to Seattle.
Vikings coach Mike Zimmer said the running back had an MRI on Monday that "went pretty well, so we'll see how he does this week."
Should Cook need to miss the Vikings' Week 6 game against Atlanta, Alexander Mattison will start at running back, a role he's filled previously in Cook's absence. Minnesota is on bye Week 7.
Cook, who signed a five-year, $63 million extension with the Vikings before the season, leads the NFL with 489 rushing yards and also has a rushing touchdown.
ESPN's Courtney Cronin contributed to this report.