The troubles of cash-strapped Kingfisher Airlines worsened today with another lender classifying its loan to the Vijay Mallya-promoted company as "sub-standard", a day after State Bank of India termed the airline as defaulter.

City-based, state-run lender Bank of India (BoI) has classified its Rs 575.27 crore loan to the Kingfisher as sub-standard, as the airline has defaulted on repayment.

When contacted, BoI Deputy General Manager (Large Corporates) Bupinder Nayyar, who handles the Kingfisher account, refused to comment. However, a bank official, seeking anonymity, confirmed the development. Bank of India has overall exposure of Rs 4,000 crore to the airline industry.

Kingfisher, which owes Rs 6,419 crore to banks, could not be contacted for response.

A bank classifies an account as sub-standard when it is close to the write-off stage. A loan turns into a non-performing asset when the borrower fails to service it for 90 consecutive days. Since Kingfisher had gone for corporate debt restructuring in November, 2010, it gets some additional days to clear the dues and make the loan a standard asset.

Yesterday, State Bank Chairman Pratip Chaudhuri said the Kingfisher account was a non-performing asset (NPA).