Robert Thomas had surgery to repair a tendon in his left wrist, and the St. Louis Blues forward will be evaluated before training camp.
He will rehab the injury throughout the offseason.
The 19-year-old, who was injured in Game 6 of the Western Conference Final against the San Jose Sharks, had 33 points (nine goals, 24 assists) in 70 games in his rookie season.
Selected in the first round (No. 20) of the 2017 NHL Draft, Thomas had six points (one goal, five assists) in 21 Stanley Cup Playoff games for the Blues, who defeated the Boston Bruins in seven games to win the Stanley Cup for the first time in their 51-season history.