Goldman Sachs made a $835 million loan to Banco Espírito Santo a month before Portugal's largest listed lender by value was bailed out in a complicated deal that could inflict losses on the Wall Street investment bank.

Because of mounting investor concerns at the time over problems at Banco Espirito Santo (BES), Goldman was unable to sell on large amounts of the debt, meaning it was left holding the bonds exposed to the lender when the Portuguese central bank took control of the bank and split it up at the start of August.

Goldman did manage to sell on an unknown quantity of the bonds to distressed debt investors before the bank was rescued. It is unclear how much the US investment bank stands to lose from the transaction.

The news emerged on the same day that auditor KPMG disclosed it had refused to approve BES's first-half report and accounts, published yesterday, citing the bank's failure to provide adequate information on its financial position and also warned of possible further losses.

KPMG, which had been hired to audit the results, said in a report published alongside BES’s accounts that these did not provide any adjustments and additional information required as a result of the rescue.

KPMG said this meant the BES report no longer provided adequate information on BES’ financial position and operations.

“... it was not possible to obtain sufficient and appropriate proof to form a basis for the present report on half-year review,” it said.

– Copyright The Financial Times Ltd 2014/ Reuters