Coach Michel Therrien announced Thursday that Pacioretty has a strained left hamstring.
The first-line left winger suffered the injury during an awkward fall in Montreal's 3-0 win in Winnipeg on Tuesday.
"It's bad luck, but it could have been a lot worse," said Therrien. "We'll take time to make sure he gets better, but it the meantime, it's not such bad news. It could have been worse."
The U.S. Olympic team hopeful has had a rough start to the season. He jammed a wrist in the opening game, but only missed one contest.
Pacioretty is know for his quick recuperation from injuries, but when asked if he would be back for the Canadiens next game Saturday against Nashville, Therrien smiled and said "This time, I don't think so."