McQuaid did not participate in the morning or pregame skates and was replaced by Shane Hnidy.
"[McQuaid] is day to day and there's nothing more to report on that situation," Bruins coach Claude Julien said before the game. "Shane Hnidy is our guy ready to play and he's certainly a possibility in our lineup tonight."
McQuaid was injured in the waning minutes of the first period of Game 2 Monday in Philadelphia when he slammed headfirst into the boards. He was taken to the hospital and returned to Boston with the team later that night.
Carter, who injured his right knee in Game 4 of Philadelphia's first-round series against the Buffalo Sabres, skated for the first time Tuesday and participated in the team's morning skate Wednesday.
"Jeff Carter looked good this morning," Flyers coach Peter Laviolette said before the game.
Hnidy had played in one playoff game this season, in the conference quarterfinal series against Montreal, when captain Zdeno Chara missed Game 2 with a virus. Hnidy said before the game that he was ready.
"It's the same as every other game," Hnidy said. "I've been taking warm-up and it's the same. I prepare to play; you never know what's going to happen. My preparation doesn't change. I get ready for the game physically and mentally."
Hnidy, 35, missed the majority of the 2010-11 season with a shoulder injury he suffered during training camp with the Phoenix Coyotes. The Bruins signed him as a free agent Feb. 26 and he played a total of three regular-season games with Boston.
This was his eighth appearance in the Stanley Cup playoffs.
"This is where experience really comes in handy," Hnidy said. "Having been in this situation before, I've been in and out of playoffs in other years. You have to stay sharp. You have to have a sense of urgency, but a calm at the same time."
Joe McDonald covers the Bruins for ESPNBoston.com.