The Australian star, a former sparring partner of Pacquiao’s, will go head to head with his American rival at Marvel Stadium in Melbourne on June 5.
Kambosos Jr, 28, famously pulled off the upset of the year after outpointing Teofimo Lopez to become the new unified 135lbs champion last November.
Pacquiao knows Kambosos better than most, having first used him as a sparring partner to help him prepare for his fight against Jeff Horn in 2017.
And he admits he was blown away by Kambosos’ enthusiasm and work ethic whilst training at Freddie Roach’s Wild Card gym together.
“I look at the training videos he has been posting on his various social platforms and I’m amazed at what he’s doing in the gym,” Pacquiao said in quotes reported by The Sydney Morning Herald.
“No-one is in better condition. 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 do not see him letting that go.
“How many world titles can he win? He’s only limited by his imagination and his ambition. So far, George has accomplished everything he has set his mind to.
“From the beginning I knew, and my team knew, George was a very good fighter. That is 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. You could sense he had big ambitions in boxing. 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 more than a sparring partner. He was a training partner.”
And after witnessing Kambosos’ dedication first-hand in training, he insists he wasn’t surprised he beat Lopez in such fashion.
He added: “George worked harder than anyone in the camp.
“I think that is why we got along so well. He would be right there with me running the hills every morning, doing sit-ups next to me after the run, full workouts in the gym every afternoon. He was always doing the extra work.
“He never cut corners on himself and it was that work ethic that showed me he had the drive to do what so few in boxing can, and that is to become a world champion.”
“The fight he took to Teofimo Lopez… I do not think anyone else could have done what George did that night.
“He showed in the Lopez fight that not only can he give out punishment, but he can also take it, and that comes from working hard every day in training and staying fit in between fights.
“George has so many strengths, physically and mentally. He is not predictable. He sees the whole ring and uses it to his advantage. He keeps everything together. He is very disciplined.”