However, the pilots' union, Vereinigung Cockpit, denied the report, saying: "At no point did the VC call for (pilots) to report ill".
Thomas Winkelmann claimed the move by almost 200 pilots to call in sick at short notice was "the equivalent to playing with fire" and would cost the troubled airline "several million euros".
In a similar incident previous year, German leisure airline TUIfly was forced to cancel flights after cockpit and cabin crew called in sick.
Shortly after the insolvency announcement bidders lined up to acquire Air Berlin's assets with major European airline Lufthansa the most likely.
The German government has provided the insolvent company with a credit facility of 150 million euros (179.8 million US dollars) to ensure continuity of operations until a buyer is found.
Air Berlin declared bankruptcy last month following years of losses and the decision of its biggest shareholder, Gulf airline Etihad, to cease payments.More news: Apple creates mail-in option for iPhone Exchange program
"We are in the middle of final negotiations with potential investors. That is crucial in order to bring talks with investors to a successful conclusion", Chief Operations Officer Oliver Iffert said in an internal memo.
Meanwhile, easyJet is keen to take on some of the routes flown by Air Berlin by buying the slots the German carrier owns at airports rather than planes. "That's the only way we can secure as many jobs as possible".
The German government has agreed to provide a bridging loan of 150m euros to keep the airline flying for three months during the busy summer season.
It is understood about six companies are in the race to bid for assets belonging to Air Berlin by the deadline this week, including Thomas Cook's Condor and low-priced players such as easyJet.
"The fear and anger among Air Berlin staff is escalating because the future of whole families is at stake".