Nearly two-thirds of Adani's debt is from overseas sources such as bonds or foreign banks, according to a report by global brokerage Jefferies.Until now, the group has mostly raised funds by using its infrastructure assets or shares as collateral. But with stock prices plunging, the value of this collateral has also dipped. The private wealth units of two big banks, Credit Suisse and Citigroup, have stopped accepting Adani bonds as collateral, Bloomberg has reported.