Cassidy said that ultimately it would be the Bruins' team doctors that make the call on whether or not Chara is given the green light.
"He was never ruled out, even the other night in St. Louis. He was ruled out for that third period - we talked about that. After that, he was going to be day to day," said Cassidy. "First thing you worry about is a concussion, because then you're in the protocol, so we avoided that - or Zee avoided that - so that was good news, and then it's a matter of, well what's next?
"I guess yesterday we got a better idea, and then this morning he's here, obviously. He's on the ice skating, so now it's real. So, that was kind of the timeline if that helps."
Grzelcyk, meanwhile, is also a possibility to rejoin the lineup. The 25-year-old was leveled from behind by Oskar Sundqvist in Game 2, causing him to be placed in protocol and miss the last two games of the series.
"I'm not really sure, " Grzelcyk said when asked if he'd be returning for Game 5. "I guess coach said a game-time decision. If I'm in, obviously I'll be ready to play and excited to join the guys again and get back to work."
Regardless of how things shake out on the back end, Cassidy is still considering playing seven defensemen.
"Depends who's in there," said Cassidy. "There's different reasons that go into that…depending on which guys are in, how much experience there is, what roles need to be divided, so we could play seven."
If that is indeed the case, a forward would have to come out of the lineup, which would lead to some double shifting.
"[Marcus Johansson] doesn't kill, so we can move a right winger around; we can move a left winger around," said Cassidy. "[Danton] Heinen's played both sides, so we're comfortable with a guy getting a few extra minutes. It gets taxing obviously if you get into extended time. We can't worry about overtimes and this and that. We're just going to play the guys that deserve to get a little extra time if we go that route."