The Irish low-cost airline has aggressively entered the German market since 2008, and currently operates flights out of 12 airports to destinations internally and across Europe.
Now the company's outspoken boss is prophesying that it's only a matter of time before his German competitors go bust.
Talking to Die Zeit, O'Leary said that Lufthansa “will shut down Eurowings in two or three years, or sell it.”
Eurowings, formerly Germanwings, is Lufthansa's low cost subsidiary which flies short-haul routes.
Lufthansa, Germany's largest airline, has been fighting rolling strikes by pilots and aircrews in recent years, as it seeks to make its business more competitive against low-cost alternatives.
Air Berlin, meanwhile, has “no strategic direction” and co-owner Etihad will try and sell off its share in the company within a few years, O'Leary claimed.
Air Berlin has well-documented profitability problems. In 2015 it recorded losses of €477 million, following on from €377 million losses the previous year.
The airline's business plans have also been hit by the massively delayed Berlin-Brandenburg airport, whose opening has repeatedly been pushed back from 2012 to (provisionally) 2017.
Bullish Irishman O'Leary also said that Ryanair will overtake Air Berlin as Germany's second-largest airline within two or three years.
“Low costs are our philosophy. We're the Aldi of air travel,” he proclaimed. “I'm hoping for a price war.”
In October the Irish carrier announced plans to start flying from Munich airport, stating that it hopes to increase its market share in Germany from 5 percent to between 15 and 20 percent by 2020.