A native of Macquarie Island - in the southwest corner of the Pacific Ocean about halfway between New Zealand and Antarctica - he's likely to have left last February, caught a current, and rode it all the way here.
But the high summer temperatures and lack of food have likely proved too much for him.
Dr Argilla said while he had improved every day since Sunday, being fed a special "fish slurry" of blended salmon and sardine, he remained critical.
"He's smaller than Happy Feet was and it's taken much more of a toll on his body. He's in a bad way - severely emaciated, dehydrated causing kidney failure," she said.
"There's a chance he could still die. It gets more positive each day but I'd probably only give a 20 - 30 per cent chance of survival at this stage.
"We're fighting against time. His organs could fail before we win."
The penguin is being treated in the zoo's native wildlife treatment room under controlled cooler temperatures.
His personality was starting to emerge, Dr Argilla said, becoming "cranky" with staff and trying to bite them, which is a sign of his growing strength.
The zoo was reluctant to give him an official name while he was still critical.
Staff are calling him 'Happy Feet junior' or 'Lovelace', the name of the crested penguin in the Happy Feet movies, voiced by Robin Williams.
But Dr Argilla believed that given he was a royal penguin, he should receive a more regal name.
A live-feed broadcast online is being considered by the zoo and it is working through the logistics.
In the meantime, it's slowly helping him return to health.
If he survives, it'll be about six weeks before he is strong enough to be set free in the South Island, to make his way back home to Macquarie Island.
