Klitschko's last defence was against Tony Thompson (left) in July
Ukrainian Wladimir Klitschko's IBF heavyweight title defence against Alexander Povetkin has been called off after the challenger hurt his ankle.
Povetkin damaged ligaments in his left ankle ahead of the 13 December bout, an injury that will prevent a return to training until the end of the November.
Povetkin, undefeated in 16 fights, is the IBF's mandatory challenger.
Klitschko, who has a 51-3 record, also holds the WBO version of the world heavyweight title.
His older brother, Vitali, beat Samuel Peter to claim the WBC belt after four years out of the ring earlier in October.
Povetkin, a former kick boxer, was super-heavyweight champion at the 2004 Olympic Games in Athens.
Like Klitschko, he also has a brother in boxing's professional ranks - Vladimir, 27, who fights at light-heavyweight.