The former education minister has called for students to pay more towards university funding in Scotland.
Students in Scotland do not have to pay tuition fees
Professor Sam Galbraith said it is unsustainable for the public purse to continue paying for higher education.
He told the BBC that increasing the current £2,000 endowment paid by graduates is the only way forward.
First Minister Jack McConnell has publicly ruled out introducing top up fees. In England new students now pay 3,000-a-year.
The comments come on the day the University of Edinburgh launched a funding campaign to raise a total of £350m from supporters and benefactors by 2011.
Prof Galbraith praised the Scottish Executive for "very generous" funding so far but said he didn't think it was going to happen in the future.
He said: "There won't be that money around any more and we will have to find it and that can only come from increasing the graduate endowment as they really are tuition fees."
Brian Laing, the St Andrews University principal, called for an independent review of university funding and a debate looking at ideas such as a graduate tax.
He said: "The political parties at the moment seem dead set on retaining the present system.
"We can't see that that's sustainable so we need a debate now if the political parties aren't going to come out and take the lead."
David Caldwell, the director of Universities Scotland, said the money from endowments paid by graduates in Scotland went to student welfare, not to funding the universities.
He also backed a review, saying Scotland had to match the rising funding levels of universities around the world in order to remain competitive.
Mr Caldwell said: "There are difficult political choices to make.
"I don't think in absolute terms its unsustainable to do it from public funds, but it's very, very difficult."
The National Union of Students Scotland said higher Education north of the border should remain free.