Reinbacher had surgery performed on his left knee Tuesday morning. His recovery time is expected to take five-to-six months.
Reinbacher left Saturday's game against Toronto due to a lower-body injury and won't return to the contest.
Reinbacher was reassigned to AHL Laval on Monday.
Reinbacher is expected to return to Kloten HC of the Swiss-A league this season, Stu Cowan of the Montreal Gazette reports.
Reinbacher penned a three-year, entry-level contract with Montreal on Wednesday.
Reinbacher was selected fifth overall by the Canadiens in the 2023 NHL Entry Draft on Wednesday.