In an interview with the New Statesman magazine, Mr Clegg, who took the Lib Dems into coalition with the Conservatives from 2010 to 2015, said Brexit had "unleashed an aggressive and regressive right-wing English Nationalism" that had taken over the Tories.
“It seems to me that the clock is now ticking for the end of the union of the United Kingdom," Mr Clegg said.
"And that the Conservative Party is converting itself into an English nationalist party. It has so little representation in Scotland, Wales, Northern Ireland and they have to compete with [Nigel] Farage.
"So I think the Conservative Party is condemned – whoever is leader – to be pulled in an ever more English and divisive direction.”
Alistair Carmichael, the Lib Dem MP for Orkney and Shetland, disagreed with his former leader, saying: “I don’t share his judgement, I don’t think that we are there yet.
“I think the lesson that most people are drawing in Scotland from Brexit is just how difficult and messy it gets when you start to unpick political and economic unions.
“If it’s difficult to break up a union that you’ve been part of for 40 years what an earth would it be like to break up a union that has stood for 300 years.”
Mr Clegg, who became head of global affairs and communications at Facebook after losing his Westminster seat in 2017, said that he expected Boris Johnson to call a general election if he wins the Tory leadership and becomes Prime Minister next week, because his political brand is based on being a "winner".
“He’s going to really scratch away at that itch because that’s all he has got," Mr Clegg said.
"That’s what columnists do – they’re trying to provoke thought. But that is not what government is about.
"Instead, you are trying to play Solomon on a whole bunch of really invidious choices where you will never keep everyone happy, where there’s no perfect solution.”