World champion Lucas Matthysse on Wednesday vowed a fight "to the death" in his July title defence against Manny Pacquiao, calling the Philippine boxing star "past his prime".
But the 35-year-old Argentine, who took the vacant World Boxing Association welterweight title in January, said it was still a "dream come true" and "an honour" to face Pacquiao, winner of eight unprecedented world titles in different weight classes.
"Obviously he is still a very great fighter but since the knockout of Marquez, I think he is not the same fighter anymore," Matthysse said at a joint news conference in Manila, referring to the Filipino's sensational 2012 knockout loss to Juan Manuel Marquez.
Pacquiao, 39, will fight Matthysse for the WBA welterweight belt on July 15 in Malaysia's capital Kuala Lumpur.
The Filipino has 59 wins with 38 knockouts in his career, and is currently a senator in the Philippine parliament. Many in the country believe he will one day run for president, but Pacquiao has insisted that he is happier in the ring than in politics.
But Matthysse, who has 39 wins with 36 knockouts in 43 matches, said he was not fazed by the status of his opponent.
"Sure, Manny has won so many titles ... I [have] only won one title. I am not going to give it up. I will die for it if I have to," he said.
"I will defend this title to the death."
Pacquiao has not fought since he lost his World Boxing Organization welterweight crown in a shock points defeat to Australia's Jeff Horn last year, and has not knocked out an opponent in nearly nine years.
He insisted, however, that he was far from finished.
"That is what I am trying to prove this coming July 15 that Manny Pacquiao is not done yet in boxing," he said.
"I keep on fighting because boxing is my passion and I love raising the flag of the Philippines."
After the Matthysse fight, Pacquiao has said he wants to take on Vasyl Lomachenko, the Ukranian superfeatherweight WBO champion currently considered by many to be the world's top "pound-for-pound" fighter.