The Bruins have been hit with injuries to start the series, particularly on the back end, going four straight games losing a defenseman to injury.
Torey Krug (lower body) and Brandon Carlo (upper body) sustained injuries in the final two games of the regular season, while Colin Miller (lower body) was injured in Game 1 and Adam McQuaid sustained an upper-body injury in Game 2.
Of all of those blueliners, Miller will be a game-time decision on Monday night.
If he is not ready to return, Tommy Cross or Matt Grzelcyk could slot in. The defensemen joined the team from Providence on an emergency basis on Monday, and took part in the pregame skate.
"Blueline looks a bit like a puzzle that we're piecing together," said Cassidy. "I guess I won't go through everybody, but Colin Miller skated this morning, so he'll be a game-time decision. We have [Tommy] Cross and [Matt] Grzelcyk both up from Providence, so one of those two could draw in if Colin can't play."
"[Adam] McQuaid didn't skate this morning, so he's, again, day-to-day, and [Brandon] Carlo and [Torey] Krug, no change in their status."
If Cross or Grzelcyk suit up, the game would be a Stanley Cup Playoffs debut.
Cross has played three NHL games, and has been a part of the organization since making his pro debut with Providence in 2011.
"It helps, the familiarity with the guys, and the area, the building, but playoffs is a different game, so I've got to be ready," said Cross.
"I've played playoff hockey in the American League. Obviously never in the National League, but the same thing down there, it ramps up a level, and I think that suits my game well, just competing hard and playing simple."
