The Norwegian faced ridicule from sections of the Scottish media about his focus on his players' diet and athleticism, but the Celtic boss believes changes have to be made for Scotland to return to the top of the football hierarchy.
Deila threatened to quit the Scottosh game if his ideas went unheard.
“If Scotland and Celtic aren't ready for these ideas, I could travel back to Norway. It's not a problem,” said Deila to The Times.
His rebuke grew stronger: "if I want to get to the Champions League, you f-----g have to look at the Champions League and if you see the fitness in the Champions League it’s unbelievable – unbelievable!
“It's not easy for a Norwegian to say this. If Louis Van Gaal came here saying the same thing, you would've been sitting there nodding agreeingly. But I come from Norway, where we are only good at skiing.”
Celtic plays Dinamo Zagreb on Thursday evening to decide who will qualify for the next round of the Europa League.