The senior guard informed Colorado Coach Tad Boyle on Sunday he would not be joining the team at the CBI tournament Wednesday when it faces Gardner-Webb.
"I said, 'How are you feeling?' He said, 'Coach, I don't want to play,' " Boyle said according to the school's website. "He's a senior. . . . I can't really comment; that's something for 'Ski.' I respect it and we'll move on. It is what it is."
Colorado (15-17, 7-11
Booker, 21, was the Pac-12's third leading scorer this season, averaging 17.2 points per game, and 18.6 points, 3.2 rebounds and 1.71 steals in conference play.
Despite Booker's sudden exit, Colorado guard Xavier Talton said he respected his teammate's decision.
Seven Pac-12 teams are playing in postseason tournaments with
Colorado is making its first appearance in the CBI, which is also experimenting with a 30-second shot clock to improve the pace of play.