The 2012 Dally M victor and 2016 premiership victor Barba had already been sacked by North Queensland after the Australia Day weekend incident which is under police investigation.
"I can't see a time at anytime in the future that he'll be welcomed back", Greenberg said of the 2012 Dally M victor, who moved to the Cowboys this season but was sacked before he ever played for them.
"If we see and can confirm violence against women from our players, we will act int he strongest of terms".
With Castle's refusal to register a player with Barba's record, the former Cowboys fullback will have limited opportunities to continue a professional sporting career.
The 2016 premiership victor had already been sacked by North Queensland over the incident which is under police investigation.
The NRL boss said he was told in great detail what the video footage from the casino showed, and that made it a simple decision to deregister the Queenslander from the league.
Rugby league standout Ben Barba, who has had stints in France and England, was kicked out of the sport in Australia on Tuesday over allegations of domestic violence. That message, I thought, had been pretty clear.
"Ben Barba will be out of the NRL immediately and I can't see him ever returning".
Although he stopped short of calling it a life ban, the deregistration effectively ends Barba's NRL career dead in its tracks.
Greenberg, who revealed he had not had any contact with Barba, said he would not call for a worldwide sanction.
We're going to get tougher and stronger on players that do the wrong thing because we can not afford the damage it does to our game.
Barba was on his last chance at the Cowboys after being forced out of the NRL in 2016 for recording his second illicit drugs strike following Cronulla's grand final win.
"I would expect that anything in relation to a situation like that, that would stand because when you're talking about issues at that level we need to make sure the codes are supporting each other".