Allegri told a news conference ahead of his side's Serie A clash at home to Empoli this weekend that 36-year-old Ronaldo informed him on Thursday of his wish to leave Turin
Juve's Champions League hopes are no longer in their hands as they head for 11th-placed Bologna needing a win and hoping rivals Napoli and AC Milan slip up.
New champions Inter Milan have booked their spot in Europe's elite club competition, with second-placed Atalanta guaranteed a top-four place by virtue of their better head-to-head record over Juventus.
AC Milan and Napoli are both on 76 points, the former holding the best head-to-head record of the pair, while Juventus are one point adrift in fifth.