"None of the possible buyers have presented a binding, fully financed offer, but there are indications of interest," Lucas Floether told German news agency DPA.

"We have set a deadline for binding offers for midday on Thursday," he said, while declining to provide details on the bidders.

Niki filed for insolvency last week after Germany's Lufthansa (>> Lufthansa Group) scrapped plans to buy its business, grounding the airline's fleet and stranding thousands of passengers.

Founder and former Formula One champion Niki Lauda, as well as tour operator Thomas Cook (>> Thomas Cook Group) and Irish budget carrier Ryanair (>> Ryanair Holdings plc), have expressed an interest in taking over Niki.

(Reporting by Ilona Wissenbach; Writing by Maria Sheahan; Editing by Douglas Busvine and David Evans)