The SNP's plans were dealt a blow by analysis from a leading independent think-tank that shows the nation will have a bigger deficit compared with the rest of the UK in 2014.
The Centre for Public Policy for Regions (CPPR) based its estimates on forecasts from the independent Office for Budget Responsibility, which recently significantly downgraded estimated tax revenues from North Sea oil and gas over the coming years.
Holyrood ministers have boasted that Scotland's stronger fiscal position in 2010/11 – the latest year for which hard figures are available – was worth £500 to each person living north of the Border.
First Minister Alex Salmond argues the smaller deficit would allow an independent Scotland to safeguard services, cut borrowing and save money for the future in an oil fund.
His Finance Secretary, John Swinney, has said the nation would be in a position to "ease the austerity".
Scotland would also have access to North Sea oil and gas revenues, 25% of which lie in Shetland's waters alone.
Jo Armstrong, of the Glasgow University-based think-tank, said: "Today's report highlights the downgrading over the past 18 months of projected North Sea tax revenues.
"For 2013-14 alone, these revenues are now expected to be only around half the level expected at the time of the 2011 Budget."
The main reason is said to be the downgrading of North Sea production levels, caused by accidents and increased maintenance work.
"As a result, not only are future oil prices difficult to predict but so too increasingly are production levels," she added.
The Office for Budget Responsibility said earlier this month that oil revenues would fall year-on-year from £11.2 billion in 2011/12 to £4.4bn by 2017/18.
Estimates for most of the period were slashed by 50% and oil price projections downgraded slightly by the body at the time of Chancellor George Osborne's Autumn Statement on December 5.
However, it stated tax revenues would be hit harder by falling production and costly investment planned by oil companies.
The CPPR said this means Scotland's deficit, relative to gross domestic product, will be above that of the UK in 2014/15.
Official figures for 2010/11 showed Scotland's deficit was 7.4 % of GDP, compared to the UK's 9.2%. It will be cut to 5.8% in 2014/15, compared to the UK's 5.2%
But by 2017/18, Scotland's relative deficit will be more than double the UK's.
The think-tank said SNP plans for an oil fund made "increasing sense" given the fluctuations in expected oil revenues, but it could leave an independent Scotland struggling to balance the books short-term.
The report's co-author, John McLaren, who once advised former Labour leader Wendy Alexander on economics, added: "Current projections for Scotland's share of North Sea taxes seem likely to leave Scotland with a marginally better, or very similar, fiscal balance compared to the UK, but only up to 2014-15.
"Thereafter, Scotland's fiscal balance is set to worsen. This position could, in the short-run at least, further worsen if a Sovereign Oil Fund was initiated in order to improve budget stability."
Ken Macintosh, Scottish Labour's finance spokesman, said: "Yet again we have another warning that basing the future of our economy on a finite and unpredictable resource is foolish and reckless.
"The SNP are already spending this money twice – on an oil fund and on filling the gap between our tax revenues and our public spending – but they do not have a plan B for the Scottish people for when oil revenues tail off after the referendum."
Scottish Conservative leader Ruth Davidson MSP said oil "should not be used as a bargaining chip by the SNP".
A Scottish Government spokesman said: "North Sea oil and gas is a fantastic asset and will continue to be so for an independent Scotland, as there is more value still to come from North Sea exploration.
"With 24 billion barrels of oil still to be recovered, with a wholesale value of £1.5 trillion, the North Sea oil and gas sector has a bright future.
"An independent Scotland will be able to face the difficult financial choices ahead from a stronger position than in the UK and use the full range of economic levers to support growth, boost revenues and deliver public services."
For the purposes of comparing fiscal balances, the figures assume all oil and gas revenues would be assigned north of the Border. Scotland's actual share would be negotiated with the UK following a Yes vote. But experts agree it would receive the overwhelming bulk of the resources.