Buchnevich took a high shoulder hit from Ottawa Senators forward Austin Watson on Tuesday with 4:52 left in the third period. Buchnevich left the game for evaluation and did not return.
When reporters asked how Buchnevich was doing on Wednesday, Blues Head Coach Craig Berube said "not very good," although he did say that Buchnevich was feeling better on Thursday.
Buchnevich is currently considered day to day.
"We lose a real good player in all aspects of the game," Berube said of Buchnevich. "He's penalty kill, power play, 5-on-5, been a very good player, a 200-foot player. Its tough. We don't want to lose a player like that, for sure."
"It's tough," teammate Brandon Saad added. "I didn't get a clean look (at the hit). He's a great hockey player. Anytime you have a guy like him go out, it's tough to fill his shoes, but at the same time, it's just a little more adversity we're facing right now, but someone has to step up (in his absence) and make a statement."
Through 50 games this season, Buchnevich ranks third on the team in points (46).