Tyler Bozak will be out at least four weeks for the Blues because of a lower-body injury.
The forward was injured in practice Tuesday, which coach Craig Berube initially called a "tweak," and will be reevaluated in four weeks.
"It's unfortunate. That's quite significant," Berube said. "… It's a loss for sure, unfortunate not only for us, but for him."
Bozak scored 11 points (three goals, eight assists) in 47 games this season.
Forwards Pavel Buchnevich and Robert Thomas could play against the Pittsburgh Penguins on Thursday (8 p.m. ET; SN360, SNE, BSMW, ATTSN-PT, ESPN+, ESPN LIVE).
Buchnevich, who scored 46 points (19 goals, 27 assists) in 50 games, has missed three games in concussion protocol but practiced Tuesday and Wednesday. Thomas, who is second on the Blues in assists (36) and third in points (48), did not play a 4-3 overtime loss to the Winnipeg Jets on Sunday because of a non-COVID-19 related illness; he took part in practice Wednesday.
"'Buchy' feels good," Berube said. "I think he'll be close to being a player. 'Tommer,' will have to see tomorrow how he feels.
"[Buchnevich] came in today and he felt good and he went and practiced and he feels good after practice. It's all good stuff going in the right direction." -- Lou Korac