Now in a race against the clock to be fit for Friday night's qualifying final against South Sydney, Manuleleua looms as an x-factor for the Knights in September.
Over the past two months, the 22-year-old has become a sensation at Newcastle.
In six games before dislocating his elbow against the Warriors a fortnight ago, the second-rower busted 23 tackles, set up five tries and scored two.
But it was only a few months ago the Kiwi found himself out of first grade, struggling to get a look in after his first four NRL games earlier in the year.
"Justin (Holbrook) and the strength and conditioning coaches sat me down one day and just told me this wasn't good enough," Manuleleua told AAP.
"They just kept me me accountable and told me this isn't good enough.
"I needed to get my weight down, I needed to get my fitness times better. And that really hit home for me.
"I was like - if I want to have a long career in NRL, I have to listen and get to work."
In just a few months since that conversation Manuleleua has dropped five kilograms, ditching the KFC during the week and focusing on muscle growth.
"They've been tracking my weight, tracking what I've been eating, and it's been working," Manuleleua said.
"The main part was my diet, obviously. I'm an islander boy, so I love eating takeout, so I was cutting down on that heaps.
"I've always been told my whole career that my talent was always there. But I never just had that work ethic.
"Attack is probably my favourite thing. But it's making those extra tackles, getting back off the line. That's what's really helped with my footy this year."
Manuleleua was named for Newcastle on Tuesday, with the edge forward needing to get through further training before being cleared to face the Rabbitohs.
It comes after fearing his season was over with a dislocated elbow against the Warriors in round 26, before scans confirmed there was no fracture.
"After the game, they took me for x-rays and the whole time I was praying, 'No fracture, no fracture'. So it was a bit of a relief.
"Everything's still surreal.
"I still can't believe the footy that I've been playing, and obviously that comes off the back of the boys giving me confidence Justin having the confidence in me."
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