Mantha will undergo season-ending ACL surgery on his knee Thursday.
Mantha sustained the injury in a 3-2 overtime win over Montreal on Nov. 5. He will conclude the 2024-25 campaign with three goals, seven points, 15 shots on net, eight blocked shots and 16 hits in 13 appearances. Mantha is eligible to become an unrestricted free agent in the summer. The Flames could move him from regular injured reserve to long-term injured reserve if the team needs the cap space.