The Bruins reported that Bergeron was one of 14 players to take part in an optional practice Friday morning.
Bergeron suffered a concussion in an April 2 game against the Ottawa Senators and returned to practice on Thursday.
"We’re certainly going to be cautious with him," Julien said. "As you know he has a history with [concussions] and we’re not about to take a gamble with him at this stage of the season.”
Boston subsequently lost Brad Marchand to a concussion in Wednesday's 5-4 win against the New Jersey Devils. The Bruins are describing Marchand's concussion as mild, and no timetable has been provided for his return.