Education Secretary John Swinney admitted there is a "very real risk" plans to hold exams could be disrupted again next year.
The Deputy First Minister told Holyrood's Education Committee the objective is still for exams to go ahead as normal in spring - but the Scottish Government faces a "dilemma" because of the risk of further coronavirus disruption for schools.
Swinney said the Scottish Qualification Authority is already working on contingency plans if exams are cancelled once again due to coronavirus.
An announcement will be made on Friday October 2 setting out the plan for exams.
At Holyrood, Swinney said: "The very real risk remains that there may be further disruptions for individual learners, individual schools and colleges, or more widely across the country during the course of the year.
"And there's no way of knowing what circumstances we will face in the spring of next year when, in normal circumstances, the exam day would take place.
"That uncertainty and risk of full disruption makes identifying a fair and robust approach an incredibly difficult decision and there are a wide range of views on the best approach to take."
He added: "Our ambition remains to run a 2021 examination diet."
The Scottish Government asked the SQA to develop a replacement grading system in the absence of exams when they were cancelled at the start of the pandemic.
But the results were condemned as unfair when it emerged pupils in poorer areas were more likely to be marked down.
An embarrassing U-turn led to marks returning to teacher estimates.
Swinney said the "plan B" preparations will not let teacher workload spiral out of control.
An SQA spokesman said: "As requested by the Deputy First Minister, SQA will now publish the outcomes of its technical consultation on modifications to National 5, Higher and Advanced Higher courses for the 2020-21 session and the 2021 exam timetable, following the publication of the Priestley Review.
"We recognise that teachers and lecturers are seeking clarity but it is also beneficial that the system receives as much clarity and certainty as possible at the one time, when all the related information is available so an informed decision about next steps can be made."
