Filipino great Manny Pacquiao on Friday pulled out of a rematch with world champion Jeff Horn, leaving the Australian looking for another challenger in his title defence.
The Queensland state government, the fight's financial backers, made the announcement two months ahead of the scheduled November 12 bout.
"We have been advised today that Manny Pacquiao... cannot return to the ring on 12 November as proposed," Queensland Premier Annastacia Palaszczuk said in a statement.
"I am advised Mr Pacquiao, who is also a Senator of the Philippines, will have other commitments at that time."
She said her government would continue to support Horn's WBO world welterweight title defence, whoever the challenger is.
The unheralded Australian stunned the boxing world with a unanimous 12-round decision over Pacquiao in Brisbane on July 2, a hotly contested result that triggered an outcry in the Philippines.
The World Boxing Organization moved to quell the controversy by re-scoring the fight with a different set of judges - who found that Horn won by seven rounds to five.
It ordered the scoring review at the request of the Philippines' Games and Amusements Board, which criticised the judges and the referee.
In the twilight of a 22-year pro career in which he won world titles in an unprecedented eight weight divisions, Pacquiao had initially called for a rematch despite US trainer Freddie Roach advising him to quit.
Pacquiao has not stopped an opponent in eight years and briefly quit boxing last year to pursue his long-held political ambitions and was elected senator.
But he quickly made a successful comeback against Jessie Vargas in November before losing to Horn.