The German carrier filed for insolvency back on August 15th
Irish carrier Ryanair has said it would be interested in making an outright bid for Air Berlin.
Its chief executive Michael O' Leary told Reuters it needs access to more data on the airline's finances.
"We would be very happy to bid for the whole of Air Berlin, which is generally a short-haul, domestic, intra-EU carrier," he said.
"But we don't know how much restructuring it will take, how much money is it losing, why is it losing so much money in a market where we make money".
Mr O' Leary also disputed comments by Air Berlin CEO Thomas Winkelmann, that a data room with information about the troubled airline had been opened as early as last May.
Ryanair has complained of a German stitch-up that it alleges will enable its chief rival in the German market, Lufthansa, to cherry-pick assets, routes and staff from Air Berlin.
Air Berlin filed for insolvency back on August 15th.
It says this was in order to continue with a restructuring process that is already underway.
The German government is supporting the company with a bridging loan, to maintain flight operations for the long-term.
In a statement, Air Berlin said: "Negotiations with Lufthansa and other partners regarding the acquisition of business units of Air Berlin are far advanced and highly promising."
The Berlin-based carrier flies to 135 destinations worldwide, but does not have any direct Irish routes.
Additional reporting: Vincent Wall