Rivera was down for several minutes before being helped from the field. Things didn't look good when Rivera was taken to the locker room on a cart.
The preliminary diagnosis was a sprained medial collateral ligament.
"When I talked to the doctors, there is a chance he could be ready for the opener, believe it or not," Sherman said in his post-game press conference. "But there's a chance he won't be, either.
Rivera earned Pro Bowl honors last season after playing with tears in both knees. He underwent surgery in the offseason.
If Rivera is unable to play vs. Minnesota Sept. 7, it will mean that the Packers have not had their starting offensive line intact since Week 2 of last season when Mark Tauscher suffered a knee injury in New Orleans (Sept. 15).