Stewart saw a foot specialist on Tuesday to get a second opinion on his lingering ankle injury, but the news was apparently not good. The 26-year-old has struggled with the injury since last season. He played only nine games in 2012, rushing for 336 yards on 93 carries shortly after signing a six-year extension worth $37.8 million.
DeAngelo Williams is expected to open the season as the Panthers' starter. Williams appeared in all 16 games last year, rushing for 737 yards and five touchdowns on 4.3 yards per carry. Sixth-round rookie Kenjon Barner and veteran Mike Tolbert will serve as change-of-pace backs. Barner got 18 carries for 49 yards in two preseason games.