The wide receiver left in the first half of the game after tearing his patella tendon, undergoing surgery yesterday.
Teammate Mike Wallace told reporters: "It's a tremendous loss. Brandon scored three touchdowns in the last two games, and we could definitely use that.
"But when Rishard [Matthews] came in the game he did a good job, and I think he'll continue to do that. You can't panic. We're not the only team this has happened to. We just have to keep pushing."
Gibson recorded 325 receiving yards and scored three touchdowns in the first half of the 2013 season.