Smith's left knee injury, sustained while trying to make a catch Sunday against New Orleans, prompted concerns he would miss the rest of the season. But Rivera calmed those fears, calling the 13-year veteran "week-to-week."
He suffered a sprained posterior cruciate ligament and will likely miss the NFC South leaders' regular-season finale against Atlanta.
Smith is the Panthers' second-leading receiver with 64 catches, good for 745 yards with four touchdowns over 15 games this season.
Carolina needs a win Sunday to claim the divisional title and a bye in the first round in the playoffs.