He suffered the injury at the end of last season and is expected to be available to skate in six to eight weeks.
Lehtera, 27, appeared in 75 regular season games with the Blues during his first National Hockey League (NHL) season in 2014-15, posting 44 points (14 goals, 30 assists) while ranking second on the club with a +21 rating.
He also added two assists in five postseason outings.