Ennis, who leads the Sabres with 39 points (21 assists), became ill Monday morning, but Buffalo coach Ted Nolan remains optimistic Ennis will be able to play against Dallas.
"He woke up not feeling really good today, maybe a touch of the flu or whatever it is. Sent him back to the hotel. Hopefully he'll be ready to go tonight," Nolan said.
Buffalo (20-45-7, 47 points) will be without right wing Jerry D'Amigo, who took a stick to the face late in a 3-0 loss at the Nashville Predators on Saturday night, an infraction that earned Nashville center Craig Smith a $5,000 fine.