Like Grzelcyk, captain Zdeno Chara's status for Game 5 is also unknown. The 42-year-old left Game 4 early in the second period after taking a deflected puck to the right side of his face and did not return to play. Chara was not at TD Garden on Thursday.
"Facial injury. No update on him," said Cassidy. "Will give you a prognosis on him [on Thursday]…he wants to play and if he was given the green light, no matter what the severity was, he'd be out there. We know that about Zee."
But, should they be without their leader - and Grzelcyk, for that matter - the Bruins will certainly need more from everybody throughout the lineup if they want to regain the series lead over the Blues.
"I think they know that more is required," said Cassidy. "Not a lot, but I think if everybody does a little bit more, not one particular player - that's what we're trying to avoid, not one guy going in and saying, 'I've got to be a hero.' I think it falls on the whole team."
Given that the Bruins have already played without Chara once this postseason (Game 4 in Carolina), as well as Charlie McAvoy (Game 1 against the 'Canes), Cassidy is confident in his team's ability to adapt.
"Our mentality will be fine in terms of being able to win without certain players because we've been there," said Cassidy. "We've done it - not in the finals of the Stanley Cup, but we did it in Carolina, the clinching game…we did it without McAvoy, Game 1 against Carolina. And we've done it without [Patrice Bergeron] this year, different guys.
"I think our guys are good that way, knowing that the team will pull together. It's just tough when you lose [Chara]. It is your captain; he plays some valuable minutes. In this particular series, you miss the actual [assets] he brings to the table. I think this team will be OK."