Krejci, who played all 82 regular-season games, was scratched with an upper-body injury prior to Boston's 2-1 win in Game 1 of the best-of-7 series on Wednesday.
"He wasn't very good today," Bruins coach Bruce Cassidy said Friday of Krejci. "We were hoping he'd skate. It didn't happen. Not playing for four days, it's going to be difficult. We hope he'll come around, but I guess I should say it's not looking good for him."
Forward Sean Kuraly replaced Krejci on Wednesday, with Ryan Spooner moving up to center the second line with Drew Stafford and David Backes.
Krejci, who played 17:56 in the regular-season-ending 3-1 loss to the Washington Capitals on April 8, had 54 points (23 goals, 31 assists) this season, and has 77 points (29 goals, 48 assists) in 93 Stanley Cup Playoff games.
