The Deputy Prime Minister accused the Ukip leader of divisive politics after Mr Farage said he would be concerned if a group of Romanians moved in next door to him.
Liberal Democrat leader Mr Clegg refused to predict how many MEPs he expects his party to have after Thursday's elections, but said Ukip would do well.
Asked about Mr Farage's Romanian comments, Mr Clegg told BBC One's The Andrew Marr Show: "The mask is starting to slip and … behind the beer-swilling bonhomie is a rather nasty view of the world. I think anyone who singles out one community, one nationality, and says 'I don't want to live next door to them', I really think that's the politics of division and I think it really should have no place in modern Britain.
"I would say to people if you don't like that point of view, if, like me, you are really put off by this very divisive, nasty approach to things, then please go out and vote. The more people don't vote, the more likely it is that Ukip will get in."
Mr Clegg said he would be happy to debate again with Mr Farage, adding: "I like to think that because I decided to take Nigel Farage on … that's one of the reasons he's being subject to more scrutiny."
Mr Farage last night admitted his choice of language about Romanian immigrants was "wrong".
He said: "I regret the fact that I was completely tired out and I didn't use the form of words in response that I would like to have used.
"I should have just hit back immediately and said 'look, understand there is a real problem here. You can't deny that too much criminality from those gangs from Romania has come to London'. I could have been clearer. But you know what? In life, sometimes we get things wrong."
Meanwhile, a leading pollster has predicted the SNP is on course to send half of Scotland's MEPs to Brussels, picking up an extra seat at the expense of the Liberal Democrats.
Professor John Curtice of Strathclyde University said recent polls pointed to the SNP taking three of Scotland's six seats at the European elections on Thursday.
As at the election in 2009, Labour would have two and the Conservatives one, he said.