Of the Rs 1 trillion, public sector banks may need Rs 930 billion, the ratings agency and research firm said in a release.
"The amount is equivalent to an equity write-down of about 1.7 per cent of the banks' risk weighted assets (RWA), and represents the loan haircut that banks may face to revive the financial viability of distressed accounts," Ind-Ra said.
"The shortfall may increase government's equity injection requirement from the Rs 700 billion announced on 31 July 2015," it said.
The access to equity will be a critical input to Ind-Ra's rating of additional Tier I bonds, as these instruments carry loss triggers linked to the bank's common equity tier I ratio, it added.
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Ind-Ra said if the corporates are able to reduce borrowing costs by 100 basis points or 1 percentage, the shortfall may reduce to Rs 760 billion from the estimated Rs 1 trillion.
Under this, banks may decide to structure their exposure, particularly to infra projects, with 80 per cent in senior debt and remaining 20 per cent as subordinate debt.
For the analysis, Ind-Ra studied 30 large stressed corporates, each with individual bank debt of over Rs 50 billion aggregating to about 7-8 per cent of the overall bank credit.
As per Ind-Ra's study, banks would need a 24 per cent reduction in their current exposure to ensure reasonable debt servicing by these corporates on a sustained basis.
"However, mid-sized PSBs will be the most affected, given their thin operating margins and weak capitalisation," it added.