Calgary Flames defenceman Juuso Valimaki sustained a torn ACL while training over the weekend and is out indefinitely.

The Flames announced Monday the injury will require the 2017 first-round pick to undergo surgery on his right knee.

"It's terrible news," Flames general manager Brad 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.

"Having said all that, it happens. It's a harsh sport and unfortunately you deal with these things. We'll deal with it.

"You're upset. You're upset for the player, first and foremost - and obviously, where we saw him fitting in with us. You absorb it and move forward. That's all you can do. You want to be there for the player, because right now he's devastated."

#Flames Defenseman Juuso Valimaki suffered an ACL injury while training... a big blow to the #Flames blue line as they were expecting big things from the young stud. Valimaki is out indefinitely — Jermain Franklin (@TSNJFranklin) August 12, 2019

The 20-year-old made his Flames debut this past season, posting one goal and three points in 24 games. He added one assist in two playoff games with the team.

The Finnish defenceman also had four goals and 14 points in 20 games with the AHL's Stockton Heat last season, his first playing professionally.

With Valimaki now expected to miss significant time in the regular season, Treliving admitted Monday the Flames will now be looking for defensive help on the free-agent market to bolster the left side of their blueline.

"We're going to be in the market," Treliving said. "The good news is that we have some young guys that we think have taken some steps, but we're certainly going to be looking at potential options on our blueline."