Manny Pacquiao (left) works out with his trainer Freddie Roach on April 1. Photo: IC

Manny Pacquiao's 21-year boxing odyssey will draw to a close in Las Vegas on Saturday with the Filipino icon aiming to cement his legacy as one of the greatest fighters in history with a decisive farewell victory over Tim Bradley.

The 37-year-old Pacquiao (57-6-2) says his third battle with American rival Bradley at the MGM Grand Garden Arena will be his last fight before he hangs up his gloves to pursue a political career in the Philippines.

The non-title welterweight showdown will be Pacquiao's first since his unanimous defeat to Floyd Mayweather in last year's money-spinning "Fight of the Century," a bout which left the eight-division world champion $150 million richer.

Pacquiao will earn another $20 million on Saturday for the final installment of his trilogy with Bradley, who stunned the Filipino with a controversial split decision victory in 2012 before losing the rematch two years later.

While stating ­Saturday's fight will be his last, he has been careful to leave the door open to the possibility of a return to the ring.

"I cannot say that I'm not going to come back," Pacquiao said, explaining that his mind-set may change once he faces up to life without the sport that has made him both fabulously rich and a national hero.

"I cannot say right now what is the feeling of retiring in boxing. I'm not there yet. I don't know how I'll feel when I hang up my gloves," he said.

Those closest to Pacquiao, including his long-time trainer Freddie Roach and the veteran promoter Bob Arum, believe he may yet return.

Arum said Pacquiao could be persuaded to prolong his career if he scores a spectacular victory over ­Bradley, who has twice gone the distance with the ­Filipino slugger.

"I think if he wins this fight well, he's going to find a way to continue," Arum said.

Roach has been in Pacquiao's corner ever since the Filipino arrived at his Wild Card gym in 2001 looking for a trainer as he prepared to embark on the US phase of his career after fighting entirely in Asia up to that point.

"It's 15 years of greatness," said Roach, who hopes Pacquiao to fight on but acknowledges that family pressures may mean his decision is final.

"His family has been pushing him to retire for a couple of years now and that's why I think it might come true," Roach said.

Pre-fight preparations were overshadowed by controversy in February when the devoutly Catholic Pacquiao described homosexuals as "worse than animals," remarks that prompted several sponsors to sever agreements with him while also drawing widespread outrage from gay and lesbian activists.

Pacquiao is adamant that the saga did not disrupt his training.

"There were no distractions," said Pacquiao, who has expressed a desire to sign off in style. "It's really important for me to win this fight ... It's part of my legacy."

Bradley (33-1-1) said he is preparing for an onslaught from Pacquiao. "He's going to come out like a bat out of hell and try to take my head off."

Bradley teamed up with veteran trainer Teddy Atlas for his most recent fight in November, which ended in a ninth-round technical knockout of Brandon Rios.