Brandon Ashley will miss the remainder of the season with a foot injury.
Ashley was averaging 11.5 points and 5.8 rebounds per game for previously undefeated Arizona.
"Last night, early in our Cal game, Brandon Ashley suffered a foot injury that will end his season," Arizona coach Sean Miller said in a statement. "While we're all disappointed, we are also aware that Brandon needs our support and positive energy surrounding him. ... This adversity will ultimately make Brandon and our team stronger moving forward."
Miller feared the injury was a broken foot after the game.
"We have to get back to the drawing board and make sure we can move forward if Brandon is not with us," Miller said shortly after the loss.
Arizona will use Rondae Hollis-Jefferson as Ashley's replacement in the starting lineup, but depth will become an issue for Miller's team.