The Filipino icon has previously worked with Kambosos Jr although it was during a time when he was not well known.
Pacquiao trained with the Australian prior to his welterweight battle against Jeff Horn in Brisbane, and the former eight-division ruler said Kambosos Jr's work ethic was something that shocked him.
"George worked harder than anyone in the camp," Pacquiao told Good Weekend.
"No one is in better condition," added Pacquiao. "You can tell he wants to keep those belts for as long as possible
"It's been a long journey for George, and he has sacrificed a lot to get to the top - I don't see him letting that go.
"From the beginning I knew, my team knew, George was a very good fighter. That's why I wanted George in all my training camps.
"It went beyond giving me good work. He 'made' me work. He was a sparring partner in name only. He wanted to be the best and he treated his sparring sessions with me as part of his education.
"I never saw the same fighter twice. He was always doing the extra work."
Kambosos Jr has home turf on his side this weekend when he collides against Devin Haney for all of the marbles.
The Aussie shocked the world last year when he dropped and outpointed Teofimo Lopez to win the WBA, WBC Franchise, IBF and WBO lightweight titles.
Haney meanwhile, has made five defences of his WBC belt but heads into the fight without father and trainer Bill Haney who was denied a visa for the Melbourne clash.