DALLAS (AP) — Cooper Flagg has been ruled out due to a sprained left ankle after the rookie No. 1 pick of the Dallas Mavericks limped to the locker room in the second quarter of the season finale.

Flagg winced as he left the court against the Chicago Bulls on Sunday night, and the Mavs soon said he wouldn't return. The 19-year-old is in a tight race with former Duke teammate Kon Knueppel for Rookie of the Year.

It wasn't immediately clear how Flagg was injured. He had 10 points and four rebounds in 10 minutes before leaving the game. He will finish the season averaging 21.0 points, 5.4 rebounds and 4.5 assists in 70 games.