They are just the latest in a series of injuries to the Panthers' defense, which has allowed 79 points during the last two games to drop to 27th overall in the league.
Johnson, who leads the Panthers with 7.0 sacks, missed portions of Sunday's loss after getting hit in the back.
Gaither missed two games with a sprained medial collateral ligament in October and re-injured the knee against Detroit.
James Anderson, one of only two linebackers from the original eight who has yet to miss a game, walked through the locker room Monday with his right foot in boot. Linebackers Dan Connor and Jason Phillips are still recovering from injuries that kept them out on Sunday. And defensive end Greg Hardy is nursing a twisted ankle, although Rivera doesn't believe it's serious.
Copyright 2011 by The Associated Press