The team says the 19-year-old's status is week-to-week.
With nine goals and six assists, Monahan is second in NHL rookie scoring behind Thomas Hertl of the San Jose Sharks. Monahan is also second in Flames scoring.
The injury bug has bitten the Flames hard this season.
Captain and top defenceman Mark Giordano remains out with a broken ankle. Forward Curtis Glenncross is out with a knee injury and so is defenceman Dennis Wideman with a fractured hand.
Forward T.J. Galiardi is day to day with back spasms. The Flames have called up centre Paul Byron from the American Hockey League.
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