Lucy Hunter, a former head of higher education and student support for the Scottish Government, said the scenario was the result of ministerial policy to reduce student grants in favour of larger loans.
First highlighted in a research paper last year, the concerns have been updated in a new analysis for the Centre for Research in Education Inclusion at Edinburgh University and the Economic and Social Research Council.
She said: "Free tuition in Scotland is the perfect middle-class, feel-good policy. In fact it benefits the better-off most, and is funded by pushing the poorest students further and further into debt."
However, a Scottish Government spokesman said the funding package tried to make the costs of studying more sustainable and easier to pay back.