Professor John Curtice of Strathclyde University said recent polling evidence pointed to the SNP winning three of the country's six places at the European elections on Thursday.
As at the last election in 2009, Labour would have two and the Conservatives one, he said. Ukip, tipped for success in England, are unlikely to secure a seat in Scotland. The clear loser would be LibDem MEP George Lyon, who is seeking re-election after a single term. "The LibDems are stuffed," Curtice said.
Support for the LibDems has nose-dived since they entered the Coalition with the Tories in 2010.
The following year they lost two-thirds of their MSPs in the Holyrood election, and in 2012 lost half of their Scottish councillors, gutting the party machine at grass-roots level.
Despite their huge influence south of the Border, where they are likely to top the May 22 ballot, Ukip remain an outside bet to pick up their first seat in Scotland, according to Curtice. He said the SNP should not interpret three MEPs as a pointer to success in September, as it would be "utterly misleading" to leap from the Euro poll to the independence referendum.
Alex Salmond last week said the election was a clear choice between the SNP and Ukip, given the two parties are fighting for sixth place, while LibDem Scottish Secretary Alistair Carmichael said it was his party versus Ukip.
"I can't see the Nationalists or Labour getting a third seat, whatever they say. I'm fairly optimistic - and this is informed optimism - that we will hold our seat," he said. But Curtice said the fight for sixth place under the proportional system was more of a three-way scrap involving the SNP, Ukip and the Tories, with the LibDems out of contention.
The SNP were the biggest winners at the 2009 European election, with 29.1% of the vote and a 9.4% rise in support, the largest increase of any party in the UK's 12 electoral regions.
The Tories, Ukip and the BNP all had their worst UK results north of the Border. Although first across the UK with 27.7% of the vote, in Scotland the Tories polled only 16.8%.
Ukip came second around the UK with 16.5% of the vote but Scotland was the only region where they polled in single figures, with 5.2%. Ukip would need twice that share of the vote to secure a seat in Scotland this week.
Labour also did relatively well in Scotland last time, holding both their MEPs and winning 20.8% of the vote, against a dire 15.7% nationally. Turnout was 28.5%, the lowest in the UK.
In the wake of a bruising radio interview on Friday which his spin doctor brought to an abrupt halt, Ukip leader Nigel Farage yesterday insisted it was not racist to say he would be concerned if a group of Romanians moved in next door to him.
In a statement, he said: "Police figures are quite clear that there is a high level of criminality within the Romanian community in Britain. This is not to say for a moment that all or even most Romanian people living in the UK are criminals. But it is to say that any normal and fair-minded person would have a perfect right to be concerned if a group of Romanian people suddenly moved in next door."
Campaigning with Deputy First Minister Nicola Sturgeon in Glasgow, Tasmina Ahmed-Sheikh, who is tipped to become the SNP's third MEP, said Farage's remarks would disgust Scots voters.
She said: "His views on where and when people should be allowed to live or use other languages are appalling - and reveal the true face of what Ukip represents."
Labour leader Ed Miliband said Ukip was not the answer to the UK's problems.
Ahead of a visit to Scotland tomorrow by Nick Clegg, former LibDem leader Charles Kennedy said his party was a positive alternative to Ukip's "lies".
Tory candidate Ian Duncan said Scots would see through Ukip as a party "that never turn up when things matter" in the European Parliament.
The poll results for the rest of the UK should become next Sunday, though in Scotland the declaration will not be until the day after as the Western Isles does not count its votes on the Sabbath.