Receiver Jordy Nelson left in the first quarter of the Green Bay Packers' preseason game in Pittsburgh after crumpling to the ground without contact on a leaping catch, a potential season-altering injury.
Nelson's initial diagnosis is a torn his ACL, according to Ian Rapoport of NFL Network. The Packers are awaiting MRI results for confirmation, Rapoport tweeted.
The Packers confirmed Nelson has a knee injury but offered no further details.
"Jordy is a key member of our team," coach Mike McCarthy said after the game. "But I'm not going to get into preliminary tests. Hoping for good news based on the information I've gotten.