Historic Scotland, which cares for 345 properties including Edinburgh and Stirling castles, predict £42m will be required over the next 20 years to protect the buildings.
Another £63m will be needed for new infrastructure and facilities relating to the estate, as well as £67m for visitor presentation and tourism, bringing the total to £172.7m. The figures are "over and above" currently allocated budgets.
Liz Smith, Scottish Conservative culture spokeswoman, said she had written to Ms Hyslop to ask why she had not disclosed it to MSPs when she recently addressed parliament on the merger of Historic Scotland and the Royal Commission on the Ancient and Historic Monuments of Scotland.
She said: "The public has a right to know the full facts."
A Holyrood spokesman said: "This is an operational work-in progress and, as such, it'd not be normal for an internal document to be presented to Parliament."