"It's terrible news," Treliving said. "It's terrible news for Juuso, and certainly, unfortunate news for our club.
"He's a really good young player who we expected to take a big step and move forward this year. It's tough. I feel horrible for him. He's had a terrific summer in terms of preparing. He was really taking some big steps forward and was excited about making an impact on our team this year."
The Flames drafted Valimaki 16th overall in 2017 and he made his NHL debut last season. The 20-year-old went on to appear in 24 regular-season games, posting three points while averaging 15:23 of ice time per contest.
Valimaki also registered 14 points in 20 AHL games with the Stockton Heat during 2018-19.