Ferguson didn't participate in Thursday's practice due to an illness, Todd Archer of ESPN.com reports.
Head coach Mike McCarthy noted that a flu bug has made its way around the Dallas locker room in recent days, with Ferguson seemingly becoming one of the latest victims. The Cowboys haven't yet suggested that the rookie tight end's availability for Sunday's game against the Packers is in any peril, but Ferguson will likely need to practice in some capacity Friday for Dallas to feel confident that he'll be ready to play.