Naoya Inoue's world super-bantamweight title fight against American WBC and WBO champion Stephen Fulton has been postponed after the Japanese boxer nicknamed "Monster" hurt his hand in training, he said on Wednesday.
The unbeaten Inoue became the first undisputed world bantamweight champion in half a century in December and was set to make his super-bantamweight debut against Fulton in Yokohama on May 7.
But Inoue's Ohashi Gym said the fight would now be moved to July.
Inoue apologised to Fulton's team for the "great trouble" his injury had caused.
"We have concluded that it would be extremely difficult for me to get into shape to enter the ring the way things are," said the 29-year-old, who has a 24-0 record with 21 knock-outs.
"It pains me to say it but this is the conclusion we have come to."
Inoue, who has won world titles in three different weight divisions, knocked out England's Paul Butler in December to become the first undisputed bantamweight world champion since Panama's Enrique Pinder in 1972.
He vacated his titles in January to move up to the super-bantamweight division.
The 28-year-old Fulton is unbeaten in 21 fights with eight knock-outs.
He is one of two world champions in the super-bantamweight division – Uzbekistan's Murodjon Akhmadaliev holds the WBA and IBF belts.