Thomas Cook's German airline Condor is eyeing a number of Air Berlin planes, as interested carriers circle the insolvent airline to secure asset sales.
According to Reuters, the leisure airline is interested in taking on a double-digit number of planes.
A source familiar with the negotiations told Reuters Condor was "in the process of preparing a concrete offer", with Condor's focus predominantly on short-haul routes, though also some long-haul ones.
Thomas Cook declined to comment.
A number of airlines are thought to be interested in Air Berlin, which filed for insolvency earlier this month after main shareholder Etihad refused to provide further financial support.
Lufthansa was immediately announced as an interested party, with Air Berlin saying when it announced its insolvency, that talks were ongoing with Lufthansa to buy parts of its business. It is unlikely to be able to pick up all of Air Berlin due to competition concerns.
Reports have said Germany's flag carrier is interested in Air Berlin's Austria-based Niki.
And Air Berlin boss Thomas Winkelmann said earlier this month that his carrier was in talks with three aviation firms at present, and plans to agree asset sales with two or more buyers by the end of September.
The German government has granted Air Berlin a €150m bridging loan to allow the airline to keep its planes flying for three months.
Low-cost giant EasyJet has also been linked with talks to buy Air Berlin assets, but the airline has so far declined to comment on any potential involvement.
Meanwhile, the chief executive of Irish airline Ryanair said this week, he would be "very happy" to bid for the whole of Air Berlin, but would need more detail to assess how much restructuring it would take.
Michael O'Leary told Reuters this week that he wanted more information on "how much money it is losing, why is it losing so much money in a market where we make money".
Ryanair has also previously expressed interest in picking up Alitalia, saying last month it had tabled a non-binding offer for Italy's flag carrier, which went into administration in May.