School officials confirmed the report late Sunday.
"Brandon needs our support and positive energy surrounding him," said Arizona coach Sean Miller. "Someone once told me, the hottest heat forges the strongest steel. This adversity will ultimately make Brandon and our team stronger moving forward."
Ashley was averaging 11.5 points and 5.8 rebounds per game. His injury will force the Wildcats to play smaller than usual. Arizona is 21-1 overall, 8-1 in the Pac-12 and, at this moment, ranked No. 1 in the Associated Press and Coaches polls.
The Wilcats play Oregon on Thursday.