The BBC Scotland pundit was speaking after Rangers' 6-1 win over Hibernian at Ibrox.
In recent years Aberdeen have been big rivals of the Ibrox side. Since gaining promotion to the top-flight in 2016, the Gers have finished behind the Pittodrie outfit twice.
The arrival of Steven Gerrard put an end to that last season, with Rangers finishing a healthy 11 points ahead while Aberdeen languished in fourth.
Now Miller has put an end to the idea of the Dons finishing second this term, believing that Celtic and Rangers are simply too far ahead of the rest now.
As quoted by BBC Scotland (11/08 live match page, 17:07), the former defender said: "I think it's inevitable that Celtic and Rangers are going to increase the gap between them and the rest this season.
"Rangers are definitely better - trying to keep up with Rangers, for Aberdeen, is going to be an almost impossible task."
It's important to remember that Aberdeen did knock Gerrard's side out of both cup competitions last season, so on their day certainly still know how to compete with Rangers. Addressing that issue will be a big aim for Rangers this term.
However the last six months certainly suggest that the gap between the Glasgow duo and the rest of Scottish football is greater than it has been since prior to financial calamity at Ibrox in 2012.
Both teams have had good starts to the season too. Celtic destroyed St Johnstone on the opening day then picked up their first win at Fir Park since 2016. Rangers meanwhile managed to rescue a win after a late scare away to Kilmarnock before demolishing Hibs on Sunday.
How it all plays out from the opening weeks will be fascinating, though none of it perhaps bodes well for the other ten teams in the top-flight, as Miller points out.
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