The pair will fight for the WBO belt at Vector Arena in less than a fortnight, on December 10.
Parker's trainer Kevin Barry said the 24-year-old heavyweight's past four years as a professional - during which he has won all 21 of his fights - has served as an apprenticeship.
Ruiz has spent eight years as a professional and is unbeaten in 29 fights.
Barry said that gives the visitor a distinct advantage.
"I've studied Andy up close. A little under four years ago I did a little bit of work with him in the gym -- there was a chance that I was going to actually end up training Andy," he said.
"I went and watched him live a couple of times perform and this was back early 2013. I thought 'this guy is destined to become a world champion'."