Minnesota's star rookie running back went down holding his knee after trying to make a cut 14-7 loss to Detroit.
The Vikings' initial diagnosis for Cook is a almost complete ACL tear, according to NFL Network's Ian Rapoport.
Last season, the Vikings destroyed their season with two brutal losses to the Lions.
Will the Lions get any respect after starting 3-1? Before he got injured, Cook ran 13 times for 66 yards and a touchdown.
Case Keenum was 16 for 30 for 219 yards passing for the Vikings in place of Bradford. Against the Vikings, that painful streak almost came to an end. While the Twin Cities Marathon weaved its way through the streets of Minneapolis and Saint Paul, the Vikings failed to do much of anything in a soul-crushing defeat to their division rivals in Week 4.
While the the Lions defense did more than hold their own today, the offense struggled against the stingy Vikings defense.
Minnesota set the tone early on defense, with Danielle Hunter sacking Matthew Stafford, the NFL's highest paid player, on the first play from scrimmage.
We won't know anything until further tests are done.
The Lions' lone touchdown came on the reach of Ameer Abdullah, whose nifty stretch across the goal line in the third quarter turned out to be the difference. The Vikings (2-2) played their third straight game without starter Sam Bradford.
"Being on this defense, I'm very blessed", Zettel said. But Thielen fumbled on the first play after hauling in an 11-yard catch. But a not-so-funny thing happened to Minnesota in its first NFC North matchup of the season against visiting Detroit. Now taking out a near 60-yard field goal attempt that fell short-they can do that anytime they want. He has four sacks through four games this season, and the MI native is looking like the next breakout star along the Lions defensive line. If the Lions can get that effort out of Abdullah consistently, Detroit's offense has a chance to be really good. But they'll need to be a whole lot better in the wake of their most recent prime time performance, no matter who's at quarterback, to beat the Vikings the way Detroit did Sunday.