United Arab Emirates' Etihad Airways and China's HNA Group were among those chief executive Hartmut Mehdorn has approached for discussions, Sueddeutsche Zeitung said in its Friday edition.
A sale of a substantial stake in Air Berlin cannot be ruled out, it added.
Air Berlin declined to comment.
Air Berlin had already pre-released third quarter results at the end of October, showing a 44 percent drop in operating profit to EUR€96.8 million ($130.97 million), hurt by an air travel tax in Germany and high fuel prices. The airline made a EUR€9.3 million operating loss in 2010.