Smith, who has scored three points (one goal, two assists) in six Stanley Cup Playoff games this season, skated early before practicing with the team. He would play on the second line with Taylor Hall and David Krejci, where he was replaced in Game 2 by Jake DeBrusk. Cassidy said if Smith plays, DeBrusk will remain in the lineup.
Smith scored 32 points (13 goals, 19 assists) in 54 games in the regular season, his first with Boston.
Tuukka Rask will start after Cassidy said that he had no concerns about the goalie's health. On Tuesday, Cassidy said Rask had some nagging injuries, but the coach pulled back from that assessment Wednesday.
"He's fine," Cassidy said. "Tuukka has been ready to go every playoff game. So there's no issue there. Someone asked me the other day, I think he just, like a lot of guys, has a few things here or there, said something. But he's ready to go. He's practicing full today. He'll be in the net tomorrow night."
Rask, who made 35 saves in Game 2, is 5-2 with a 2.06 goals-against average and a .930 save percentage in seven playoff games.