Proposals by Ucas to reform the university entry system across the UK would require Scottish pupils to sit school-leaving exams earlier and finish them before the end of May.
They would also cut the marking time from eight to four weeks to release results at the beginning of the summer holidays, in early July.
A consultation paper issued by Ucas this week, reviewing the admissions process, would have serious implications for the Scottish system just as new qualifications are coming on stream, it has emerged.
If adopted, it could be implemented at the same time as the first cohort of pupils are due to sit the revised Highers under Curriculum for Excellence and apply to university - in 2016.
Pupils sitting a Higher in one year face a "two-term dash" under current time-tables. Fears are now being raised that if exams were brought forward to even earlier in the year, the only feasible timeframe would be to spread Highers over 18 months.
Education Secretary Michael Russell welcomed plans by Ucas to simplify the system, eliminate some of the problems faced by non-traditional applicants, and tackle "the lottery that is the clearing system".
But at a Ucas conference in Edinburgh on progression to higher education in Scotland, he warned the admissions service that the conclusions of its review would have to be "supportive of our direction of travel" and take full account of the differences that exist north and south of the border.
The report recommends a move to a system of "post-qualifications applications".
But Mr Russell said Scotland already had such a system as most Scottish students achieved their qualifications in S5 and did not leave school until S6.
Many in Scotland see the Ucas review as a bid to solve a largely English problem. Mary Curnock Cook, chief executive of Ucas, said less than 10 per cent of UK applicants have three accurate predictions of the grades they will achieve and 30 per cent have one under-prediction.
Mr Russell said the Highers exam diet runs until June and Scottish results are not published until August: "This timetable is already tight, with considerable pressures for schools, the Scottish Qualifications Authority, and universities."
He added: "I can see clear benefits in having a system that is easier to understand and that is more accessible to non-traditional applicants. However, it is not yet clear to me how these and other benefits will be realised in Scotland by squeezing timetables that will have knock-on effects in other parts of the system."
Janet Brown, chief executive of the SQA, said: "We are moving to a more flexible qualifications system. That pattern may change but we have got to ensure it is achievable within the new Ucas timeframe."
Ken Cunningham, general secretary of School Leaders Scotland, said if Scottish exam results were released in early July - as Ucas proposes - pupils would not be able to access valuable support from school staff as teachers would be on holiday.
Ucas said: "It is not possible to implement a post-results system without a change to the current timetable of admissions. However, we believe the changes are manageable and are shared by all the key elements in the process."
Original headline: Ucas reform plan could pile pressure on Scottish system