The Dallas Mavericks' first draft pick limped to the locker room during the second quarter of the final regular-season game. This also marked the last game for Dallas, as they did not qualify for the playoffs.
Flagg was visibly in pain as he left the court during the matchup against the Chicago Bulls, and shortly after, it was announced from Dallas that he would not return to the game.
The 19-year-old is in a tight race with his former Duke teammate Kon Knueppel for the Rookie of the Year award.
It was not immediately clear how Flagg sustained the injury. Before exiting, he scored 10 points and recorded four rebounds in 10 minutes on the court. He will finish the season averaging 21.0 points, 5.4 rebounds, and 4.5 assists over 70 games played.
Dallas finished the season in 12th place in the Western Conference with 26 wins and 56 losses.