Ellington left Sunday's win over the New Orleans Saints early after hurting his knee on a non-contact play. He was taken to the locker room on a cart and did not return.
Ellington ran 12 times for 69 yards and a touchdown before the PCL sprain. Chris Johnson, who is listed behind Ellington on Arizona's depth chart, took over as the team's top back Sunday.
Ellington led the Cardinals with 660 yards rushing in 2014, playing in 12 games because of a hip injury. He also caught 46 passes for 295 yards.
The Cardinals take on the Chicago Bears in Week 2.
– Rohan Nadkarni