The Canadiens defenceman has been ruled out of the first four games with an upper-body injury.
General manager Marc Bergevin wasn't specific about the injury when speaking with reporters on Wednesday, but the 22-year-old Beaulieu reportedly isn't dealing with a concussion.
"To protect the player, you hide things," he said. "You don't want the player becoming a target later in the playoffs. This is nothing new."
Beaulieu, 22, hasn't played since Ottawa defenceman Erik Karlsson checked him in Game 3 of their first-round series.
The native of Strathroy, Ont., had one assist in the first three games against the Senators.
Greg Pateryn is expected to remain in the Montreal lineup for Beaulieu. The 24-year-old didn't have a point in 17 games with the Canadiens in the regular season but responded with an assist in each of the final two games versus Ottawa.