Receiver Jordy Nelson left in the first quarter of the Green Bay Packers' preseason game 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.

It would be a devastating injury for one of the team's most important players. Nelson had the best season of his career in 2014, following the four-year, $39 million contract he signed entering training camp. He finished seventh in the NFL with 98 catches, fourth with 1,519 yards and tied for second with 13 touchdowns.

If Nelson misses significant playing time, slot wideout Randall Cobb would be elevated to the team's No. 1 receiver spot. Cobb, a free agent this offseason, signed a four-year, $40 million deal in March to return to the Packers. Second-year receivers Davante Adams and Jeff Janis, along with rookie Ty Montgomery, would also likely have increased roles on offense.

However, Nelson provides a unique dynamic in the Packers' passing game. His ability to stretch the field on vertical routes is irreplaceable, as is his familiarity with MVP quarterback Aaron Rodgers.