Hypo Real Estate Holding said a German shareholder has filed a court case against the company to challenge the legality of its acquisition of Depfa Bank.
A statement said a court in Munich will only rule upon this suit after completion of the transaction.
"Hypo Real Estate Holding AG believes that the announced proceedings have no merits and intends to complete the transaction on schedule," it said.
"The announced proceedings will not trigger a statutory block of the commercial register to prevent the registration of the intended capital increase," it added.
Hypo Real Estate has proposed a €5.7 billion acquisition of Dublin-based Depfa Bank by offering €6.80 and €0.189 new Hypo Real Estate shares for each Depfa share, valuing each share of Depfa at €16.14.
To fund the purchase, Hypo Real Estate will increase its capital by about 50 per cent by issuing 67 million new shares, meaning some 58 per cent of the purchase price will be covered by new equity.
The remaining share of the purchase price will be in cash, which Hypo Real Estate plans to raise through a €450 million mandatory convertible bond.