The Liberal Democrats are fighting the European elections in "challenging circumstances" due to the "difficult decisions" taken in coalition government, according to Nick Clegg.
The Lib Dem leader, whose party is trailing in the polls, refused to make any "crystal ball-gazing predictions" ahead of Thursday's vote.
Mr Clegg was in Edinburgh to give a speech to business leaders in his capacity as Deputy Prime Minister before giving interviews ahead of the elections.
He was joined by Scottish Lib Dem leader Willie Rennie, and the party's only Scottish MEP George Lyon.
Questioned by one member of the audience about what would be an acceptable result for his party, Mr Clegg said: "An acceptable and desirable result would be as many Liberal Democrat MEPs returned to the European Parliament as possible, but I have been in politics long enough to know that my role is to lead my party, not to make statistical, crystal ball-gazing predictions.
"But clearly in elections, it is stating the flaming obvious, we are fighting in more challenging circumstances than when we fought last time.
"The last time George (Lyon) was elected was in 2009 before we went into coalition and before we took all of these difficult decisions to repair and reform the economy as a whole."
Mr Clegg refused to be drawn any further when questioned on recent polling later, stating: "I am simply not going to make predictions about an election that has not happened yet."
"I am not a pollster. I am not a soothsayer. All I can tell you at the moment is what we stand for.
"You have only got the Liberal Democrats... saying look, sure there are things we need to change.
"But we can't do any of those things unless we work together both within the UK and with other countries in Europe. That's the message that I believe in the long-run will prevail."
During his speech, Mr Clegg highlighted the opportunities for further devolution in the event of a No vote in the referendum.
He said his party would "act as the guarantors" of more powers for Scotland if it rejects independence.
But any final settlement would have to be negotiated with the other pro-UK parties, businesses, civic Scotland and the SNP if they are willing to embrace devolution, Mr Clegg said.
The Lib Dems want Holyrood to raise half of its own revenue and set its own rates of income tax, capital gains tax and inheritance tax.
"I think what is significant right now is the really quite unusual consensus that has emerged across all parties that a further process of devolution should happen," he said.
On the involvement of the SNP, he added: "Clearly they will have to overcome their disappointment that they haven't secured their cherished goal of putting Scotland out of the UK.
"But I hope they will be able to overcome that relatively quickly and not take their bat and ball away.
"The more we can secure a broad-based consensus, the more likely that it is going to happen both quickly and on the most ambitious scale."
SNP MSP Annabelle Ewing said: "Given that Mr Clegg's party have been promising Home Rule for over a hundred years, people in Scotland are unlikely to view them as the guarantors of anything - except continued Conservative rule from Westminster.
"Let's not forget that, as recently as 2011 the Lib Dems had the chance to beef up the Scotland Bill with a raft of new economic powers that they had previously supported - but they reneged on their previous commitments.
"With such a track record, it is little wonder that the Lib Dems are currently fighting it out for sixth place in the European elections in Scotland.
"Scotland is an immensely wealthy country, richer per head than the UK, France, Italy and Japan - but only a Yes vote in September is the only way to guarantee that Scotland gets the vital job-creating powers it needs to build a fairer, more prosperous society."