Pacioretty suffered the injury in the third period of Friday night's win over the New York Islanders. He was the subject of trade rumors ahead of the Feb. 26 trade deadline but denied reports last week that he requested a deal to a new team.
The Canadiens also will be without defenseman Victor Mete for six weeks after he suffered a broken finger against the Islanders. Pacioretty entered Friday with 17 goals and 20 assists in 63 games this season. The 29-year old has scored 30 or more goals five times in his career, all with the Canadiens. His career high is 37 in 2014-15.
Mete has seven assists in 49 games for the Canadiens in 2017-18.
The Associated Press contributed to this report.