Pacquiao (right) gave a boxing masterclass against Cotto last year
Manny Pacquiao believes a fight against bitter rival Floyd Mayweather Jr will happen later this year.
Plans for the pair to meet fizzled out last week after a row over Mayweather's demands for random blood and urine sampling in the build-up to their bout.
World welterweight champion Pacquiao will fight Ghana's Joshua Clottey in Dallas in March instead of Mayweather.
But he said: "It will happen. I'm still hoping a fight with Mayweather will be pushed through, maybe by summer time."
The Filipino said Mayweather's drug-testing demands unfairly cast him in a bad light as a suspected cheat.
He added: "I want to clear my name because I'm a very honest person. I'm very disappointed for what he accused me of. I'm clean. I'm not cheating. I'm a very honest fighter."
His trainer, Freddie Roach, is also optimistic the fight will go ahead.
"I think it's going to happen," he said. "Maybe Mayweather is up to doing this to get more press, I don't know."
Pacquiao's promoter Bob Arum said on Sunday that he also believed a fight at some point against Mayweather had not been totally ruled out.
"There's always later in the year and next year, it's up to Mayweather," stated the Top Rank impresario.
"But if he starts this nonsense again with testing or anything then let him take a walk.
"We are not going to get into a debate with him ever again on stuff that we know nothing about and that only regulators really can understand.
"We have commissions who regulate this sport. If [Mayweather Jr] wants any special testing he should address it to the commission that will have jurisdiction over the fight."
It was confirmed on Sunday that Pacquiao's will defend his WBO welterweight belt against Clottey at Cowboys Stadium in Dallas on 13 March.
Top Rank spokesman Lee Samuels said the state-of-the-art arena will be configured to seat 50,000 fans for the fight, but the capacity could be raised or lowered.
Arum insisted that Clottey, who beat Zab Judah for the IBF welterweight title in August 2008, will be a tough opponent for Philippines star Pacquiao.
"He's a real strong, aggressive and hard punching African and he poses a real test for Manny," he said.
Clottey, 32, lost a split decision to Puerto Rico's Miguel Cotto last June. He has a 35-3-0 record, with 20 wins by knockouts.
Pacquiao stopped Cotto in Las Vegas in November to become a five-weight, five-time world champion.