"Great crowd there on Saturday, great game of footy, (but) it's particularly disappointing that one person can spoil some of those headlines."
Greenberg praised Penrith for reacting swiftly on the incident, with the club expected to identify the person over the next 24 hours.
"I give the Panthers club, people like Brian Fletcher and Phil Gould an enormous wrap for working effectively round the clock for the last 48 hours, trying to find this culprit," he said.
"And if we do, we'll throw the book at him.
"The message is simple: we don't tolerate that sort of behaviour. Nor does community, or rugby league, more specifically.
"You're not welcome in our game. You're not welcome to be part of the game. In fact, you aren't part of the game. If and when we get to that point in time, we'll make those decisions."
Kangaroos coach Mal Meninga said he was angered by the incident.
"We thought racial vilification has gone out of our game, obviously it hasn't," he said.
"I reckon Greg will be hurting. I applaud him for his actions and hopefully they find the perpetrator and kick him out for life."
The Panthers have also denied reports utility Tyrone Peachey was racially vilified in the same game.
