The experienced Melbourne Victory and former Brisbane Roar coach said while he had never seen anything to raise his suspicions, that was no reason to be fooled into thinking it wouldn't happen.
"Of course it is," Postecoglou said on Thursday, when asked whether the league was vulnerable.
"We're talking about money. It can corrupt the most stable of environments."
Postecoglous was speaking soon after the release of the findings of a year-long Australian Crime Commission investigation which found widespread use of banned drugs in Australian professional sport and links with organised crime.
The report said the links may have resulted in match-fixing and fraudulent manipulation of betting markets.
Postecoglou said all sporting clubs such as the Victory could do was create a good culture, educate their players and staff and recruit the best people they could.
But even then constant vigilance was needed.
"There's no point being oblivious to it or saying it doesn't happen in our sport," Postecoglou said.
"Because I think it's proven it does happen in our sport. It does happen in all sports and in all cultures and all walks of life."
He said there was no reason why match-fixing would be less likely to happen in Australia than anywhere else.
Postecoglou took a similar view on performance-enhancing substances, saying he had seen nothing suspicious during his career but constant vigilance was needed.
He said the Victory's emphasis on the technical, rather than physical, aspects of the game should safeguard them to an extent, but the ACC findings should act as an alarm bell for everyone.
Postecoglou said no sport's anti-doping code would be enough in itself to insulate them from performance-enhancing drugs.
"Even the strongest, it comes down to dealing with human beings and if people want to find loopholes they'll find loopholes in everything," he said.
"All you can do is drive your own program, stay vigilant, stay on top of it, have a culture where we're not interested in crossing any lines that don't need to be crossed."