The trustee in the case of the bankruptcy of David Drumm has claimed that Anglo Irish Bank's entire claim on Mr Drumm is based on a fraudulent premise.
The Boston attorneys say Anglo Irish gave its former chief executive the money to buy shares in his own company.
They said as this was illegal it negates their claim of more than $10m (€8.5m) on Mr Drumm.
Mr Drumm left Ireland two years ago and filed for bankruptcy in Boston, Massachusetts, where he now lives with his family.
He claims he cannot repay his debts, has returned two expensive cars to the dealers and filed for bankruptcy.
