Monahan, who did not participate in practice yesterday or morning skate today, is being listed as day-to-day by the team. Josh Leivo will take his place against the Edmonton Oilers
The 26-year-old centre has picked up two goals and 10 assists in 16 games this season.
Live coverage of tonight's game between the Flames and Oilers starts at 9 p.m. ET on Sportsnet.