Leaf suffered the injury during the No. 3 Bruins' victory over Washington on Wednesday. He stepped on the foot of a Huskies player as they came down for a rebound and was helped off the court by two staff members.
He had been using crutches and wearing a boot in hopes of playing Saturday.
The 6-foot-10 forward is UCLA's second-leading scorer (16.1 PPG) and rebounder (8.5 RPG).
UCLA is guaranteed a top-three seed in the Pac-12 tournament. After Saturday, the Bruins' next game will be in the conference quarterfinals Thursday.