The 27-year-old Berglund was hurt in training for the upcoming season. He dislocated the shoulder during the 2013-14 season.
He had 12 goals and 15 assists in 77 games last season and had two goals and two assists in six playoff games.
Berglund was a first-round draft pick of the Blues and the 25th overall selection in 2006. He has 247 points in 513 regular-season games and 13 points in 29 postseason appearances.