Strathclyde University's Fraser of Allander Institute, noting household spending had been the main driver of recent growth in Scotland as well as in the UK as a whole, raised concerns over how this was being funded.
In its latest commentary, published yesterday, it cites the need for an improvement in net exports and business investment to ensure a durable recovery. And it highlights the difficult back-drop of the Coalition Government's austerity programme, and a continuing fall in real household incomes as pay growth continues to lag inflation.
Professor Brian Ashcroft, economics editor of the Fraser of Allander commentary, said: "Some households seem to be having to have recourse to cash generators, payday loan companies, and pawnbrokers.
"If you look at the Scottish streets, these are increasingly important (in) allowing many people to get their assets into cash very easily. To the extent that is supporting household spending, it is not going to last."
He noted that new car purchases were up but added that a "far greater proportion"were being financed by credit, with lease arrangements also common. He said this would be fine if household debt were low but highlighted the fact that it was high.
Mr Ashcroft declared that it was a "big concern" that business investment was "still pretty flat".
While noting business surveys were painting a more upbeat picture, he added: "It is not being backed by people putting money where their mouth is, in investment terms."
He cited signs that big companies were building up their cash reserves and buying back shares, rather than investing, to try to push up returns on equity, observing that this was what corporate leaders' bonuses were based upon.
Fraser of Allander yesterday raised its forecast of Scottish growth this year to 1.3%, from 0.9% in its previous commentary in June.
It raised its forecast of expansion in 2014 to 1.8%, from 1.6% in June, and held its growth projection for 2015 at 2.1%. The Scottish economy grew by 0.4% in 2012.
Mr Ashcroft noted forecast growth for 2014 was still adrift of Scotland's longer-term annual trend rate.
Against a back-drop of below-trend growth, Fraser of Allander is forecasting that the unemployment rate, on the International Labour Organisation measure, will rise to 7.6% by the end of 2013 and to 8.3% by the close of next year, before falling back to 6.9% by the end of 2015. Figures published earlier this month by the Office for National Statistics showed that ILO unemployment in Scotland was 201,000, a rate of 7.3%, in the June to August period.
Summing up the position in its latest commentary, Fraser of Allander says: "There is little doubt that, five years since the start of the Great Recession, we are now witnessing a stronger recovery, albeit belatedly compared to any recession in the last 70 to 80 years. And there are good reasons to be hesitant about whether the recovery can be sustained. Nevertheless, the Scottish economy has grown for five successive quarters to the second quarter of this year. The UK has grown for three successive quarters to the third quarter of the year. And the growth rate has been rising as 2013 unfolds."
Mr Ashcroft highlighted his relief that the threatened closure of the Grangemouth petrochemical plant had been averted, after a last-minute deal between owner Ineos and trade union Unite.
Fraser of Allander estimates in its commentary that closure of the petrochemicals plant would have reduced Scottish gross domestic product by about 0.7%, given the knock-on economic impact, and cost 4240 jobs in total. It adds that closure of the whole Grangemouth site would have led to a 1.2% fall in Scottish GDP, and the loss of 7261 jobs.
Fraser of Allander says the performance of the financial services sector "continues to give cause for concern". However, it highlights the fact that the manufacturing sector in Scotland has enjoyed a better performance than that in the UK as a whole in recent times.
Paul Brewer, senior partner at accountancy firm and commentary sponsor PwC, welcomed the fact that Scotland was among the best-performing parts of the UK outside London and the south-east of England.
However, declaring that the private sector should "take courage and invest", he added: "Recovery based on consumer spending, against a continuing background of weak real incomes, is unsustainable."