Pacquiao and Mosley were in New York on Monday to wrap up a three-city press tour promoting their fight, which will air on pay-per-view May 7 from the MGM Grand in Las Vegas.
Fans have been clamoring the past couple years for Pacquiao to face Mayweather in what could be the richest fight in boxing history.
But Mayweather has been reluctant to face Pacquiao, and he's now in legal trouble that could prevent the matchup from ever happening.
"I don't know what to make of Floyd not fighting this fight. It's mind-boggling to me," said Mosley, who lost a lopsided decision to the unbeaten Mayweather last year. "It's like I said on Twitter, it feels like I'm doing Floyd's dirty work."
Mosley thinks part of the reason Mayweather hasn't fought Pacquiao is that he's a southpaw, and left-handers have caused Mayweather trouble in the past.
But the bigger issue appears to be legal: Mayweather is accused of felony grand larceny, coercion and robbery from an incident last September, and also faces misdemeanor domestic battery and harassment charges.
There's no telling how long it will take those issues to be resolved, and no guarantee Mayweather will ever step in the ring again, much less against Pacquiao.
"What I have done in boxing, I am satisfied, I'm happy, and I'm not really pushing that fight hard," Pacquiao said Monday during an interview at The Associated Press. "If that fight happens, that's good for me and the fans, because the fans are very eager to see that fight.
"People want to see a good fight," he said moments later, "between me and him."
For now, though, they'll have to settle for one against Mosley.
The former five-time champion split with Golden Boy Promotions, of which he was part owner, just to land the opportunity against the sport's most bankable star.
Mosley even lobbied at the home of Pacquiao promoter Bob Arum that he should be chosen for the fight.
Now, the 39-year-old Mosley is defending himself against fans and critics who believe he's too far past his prime to give Pacquiao much competition.
After all, Mosley was nearly shut out by Mayweather last May and managed only an uninspiring draw against Sergio Mora in September.
"I'm sure there will be other opportunities," Mosley said, "but this is a fighter who is supposed to be one of the best in history. To take him out would be remarkable."
Mosley isn't the only one coming to his defense.
Arum called him "the epitome of what we like a fighter to be," and Pacquiao trainer Freddie Roach said that it's hard to get motivated for a guy such as Mora.
Meanwhile, Pacquiao gushed over all that Mosley has accomplished, calling him one of the best of his generation.
"I respect and I really admire Team Mosley, because this is my first time to encounter an opponent where they're not talking trash," Pacquiao said. "In the ring, we'll have to forget we're friends and do our job and give everybody a good fight."
Pacquiao plans to spend about four weeks training in the Philippines, which allows him to spend time with his family and tend to his political career; he was elected to Congress from the Sarangani province last year.
Then he'll head to the Wild Card Boxing Club in Los Angeles for about three weeks, before jetting off to Las Vegas for the week of the fight.
It'll be the first time Pacquiao fights in Las Vegas since 2009, after fighting twice last year at Cowboys Stadium near Dallas.
Tickets at the MGM Grand had nearly sold out by Monday, and closed-circuit tickets at casinos on The Strip are already on sale.
"I always said that the best matchup would be Shane Mosley and Manny Pacquiao," said Nazim Richardson, who will train Mosley for the fight and who joined the chorus of praise for boxing's current standard-bearer. "This guy has been one of the best in history.
"If you don't like Manny Pacquiao," Richardson said with a smile, "then he must have done something to you personally, because it's impossible not to like Manny."