What is the silent fiscal crisis that is being talked about these days?

Fiscal crisis is about a rising fiscal deficit. Normally, fiscal deficit rises due to spending going out of control. Recently, Rathin Roy of the PM Economic Advisory Council made a statement that the silent fiscal crisis for India could arise from weak tax revenues not from higher spending. He was hinting at weak tax collections on the direct tax front and the GST front where the shortfall was nearly Rs.2,00,000 crore overall.