On Sunday night, 12 European clubs, including Barcelona, Real Madrid, the Milan giants and Manchester United, released a statement detailing their plans for a breakaway competition.
The proposals would see 20 teams take part in two groups followed by a knockout stage.
Fans, pundits and even players have hit out at the idea which has been condemned by Uefa.
McCoist, when asked whether Celtic and Rangers should be allowed to take part, hit out at the plans.
"I'd be so against it,” he said on talkSPORT. “I just hate the principle of it, I really do. I think it's unfair.
"Do you know something? I just hope that the backlash from the public effectively makes them sit back and think.
"I wouldn't be too sure it will by the way, I have to tell you. But you would just hope it does make them think 'wait a minute, we might have got this one wrong'."
A statement from the founding clubs noted the league would "significantly greater economic growth and support for European football via a long-term commitment to uncapped solidarity payments which will grow in line with league revenues."
Uefa have threatened to ban players from appearing at international level.
"The clubs concerned will be banned from playing in any other domestic competition, European or International level, and the players could be denied the opportunity to represent their national teams."