Manny Pacquiao, who has been world champion at eight different weights, says his next fight will “answer” whether he should continue boxing.
The 39-year-old will face Argentine Lucas Matthysse for the WBA welterweight title on 14 July.
He has not fought since unanimously losing the WBO version of the belt on points to Australian Jeff Horn last July.
“If my body does not respond anymore why am I pushing myself?” he said.
“This fight is the answer of all those questions.”
Pacquiao has replaced long-term trainer Freddie Roach with Buboy Fernandez for the contest in Kuala Lumpur, Malaysia.
Matthysse, 35, has won 36 of his 44 fights by knockout.
Pacquiao, who is preparing for his 69th professional fight, was the first boxer in history to win world titles in four of the original eight weight classes of boxing – flyweight, featherweight, lightweight and welterweight.
In 2015 he was beaten by Floyd Mayweather in a Las Vegas bout billed as the most lucrative fight in history.
Pacquiao said “it is possible” that a re-match could take place with the American, who announced his retirement after beating mixed marital arts fighter Conor McGregor in another big-money boxing bout last August.
“As long as he will come back and continue fighting there is a chance,” he added.
Now a senator in the Philippines, he pulled out of rematch with former schoolteacher Horn, 30, last September, and had been advised to call time on his career by Roach, who had worked with him since 2001.