Green issued an attack yesterday on the SPL's proposed new three-tier, one-governing body proposal which was tabled at the start of this week.
The Gers supremo also referred to a new Dutch/Belgian League that has recently been mooted and the possibility that a European League may be realised at some stage as possible escape routes for the Ibrox outfit from the Scottish game.
But while Macmillan has no doubt his club's chief executive is right to raise the prospect of a breakaway, he admitted it is not a realistic one, not least because of matters of finance.
The general secretary of the Rangers Supporters' Association said: "The bottom line is that I fully back Charles Green's right to explore other options for the club and I can fully understand his anger.
"It is not right that Rangers, the biggest club, or at the very least one of the two biggest clubs in the Scottish game, do not have a say in what is going to happen with it and how it will be changed.
"But while I feel it is ridiculous that we seem to be punished for the acts of others, realistically we are going to have to accept that we are playing in the Scottish game for the foreseeable future."
Looking at both the continental option and the English route, Macmillan is anything but optimistic.
He said: "Do you think that Wigan or Aston Villa would vote to have us in when it would put their own positions in the most lucrative league in the world at risk?
"That situation would be repeated in whatever league we might want to play in down south, whether it were the Championship or the Premier League.
"Looking at Europe, I think there are so many obstacles to cross-country leagues.
"But how many fans could afford to be travelling across Europe every other week to watch us play Dutch or Belgian clubs? How many would want to?
"In the past we have had the likes of the Atlantic League being mooted but it came to nothing.
"The fact is that while it may be viable for Dutch and Belgian clubs, who are in close proximity to play each other, we are a long way off.
"Being realistic, our prospects of leaving the Scottish game are not high."
He added: "Yet. while all of this is voted on. Rangers have no say on any of it. And that is something that is just not right."