The Bank of Portugal said negotiations had broken down with an unidentified potential buyer.
Novo Banco was set up in August 2014 to salvage assets from the failed Banco Espirito Santo (BES), after a â‚¬4.9bn (Â£3.6bn; $5.5bn) state-led bailout.
The central bank said it would now start talking to another bidder.
The Portuguese government put up most of the cash to rescue and restructure BES, but â‚¬1bn came from other Portuguese banks, who will be repaid from the proceeds of selling Novo Banco.
The government began the process by drawing up a list of three unnamed bidders for the bank and had intended to sell it to the highest bidder by the end of August.
Portuguese news media have named the three bidders as two Chinese companies, Anbang Insurance and Fosun International, and a US firm, Apollo Global Management.
Portugal's central bank has missed its deadline to sell Novo Banco, a bank created after the collapse of the country's second-biggest lender.