Sundqvist suffered the injury with 1:07 left in the first period of Friday's 2-1 shootout win in San Jose. He left the game and did not return.
"He's an all-around player for us, lots of different situations and penalty kill and power play, checking, energy and really our team feeds off him," Blues Head Coach Craig Berube said of Sundqvist "It's a tough loss, for sure. We're going to miss him, but we've got guys who are going to come in and fill in. Everybody just has to pick up the slack, that's all you can do.
"It's unfortunate. It's tough news for Sunny and us, obviously."
Blues General Manager Doug Armstrong said in a release that Sundqvist will require surgery when the team returns to St. Louis. He will be re-evaluated at training camp for the start of the 2021-22 season.
Through 28 games this season, Sundqvist has posted four goals and five assists (nine points).
