The International Olympic Committee rejected a special request for Pacquiao to take part, the Philippine Olympic Committee announced Sunday.
Pacquiao, who hung up his gloves in 2021 before an unsuccessful presidential run, said he respected the decision of the IOC, which has an age limit of 40 for Olympic boxers.
"While I am very saddened and disappointed, I understand and accept the age-limit rules," said a statement from Pacquiao, who won world titles at eight different weights during a glittering professional ring career spanning more than a quarter of a century.
The Philippines last year asked the IOC for a "universality place" for Pacquiao, who has never boxed in the Olympics.
Universality places are usually awarded to athletes from smaller countries who struggle to secure slots in the Olympics through normal qualification.
Philippine Olympic Committee president Abraham Tolentino claimed Sunday the IOC decision would deprive the country of a "sure podium or first ever gold" in Olympic boxing.
Pacquiao said he will continue to support and cheer for Filipino athletes competing in the Olympics.
He also reminded his fans that despite his retirement, he intends "to bring pride and honour to my country inside the boxing ring in the near future".
A Pacquiao aide confirmed to reporters Monday that Pacquiao will fight Thai kickboxer Buakaw Banchamek in an April 20 exhibition match in Bangkok.
The match against Muay Thai great Buakaw will be fought under international boxing rules, the aide said.
