He suffered the injury during the Blues' 3-1 win over the Tampa Bay Lightning on Tuesday.
The surgery will be performed by Dr. Charles Goldfarb of Washington University Orthopedics and Blais will be re-evaluated in 10 weeks.
Blais, 23, is currently in his third season with the Blues after the team drafted him in the sixth round (No. 176 overall) of the 2014 NHL Draft. This season, 6-foot-2, 205-pound forward has appeared in 20 games, posting eight points (five goals, three assists) and 10 penalty minutes.
Overall, the Montmagny, Quebec, native has accrued 15 points (eight goals, seven assists) and 22 penalty minutes in 63 career regular-season games with the Blues.
During the 2019 postseason, Blais tallied a goal and two assists in 15 games, helping the Blues capture the Stanley Cup Championship.
