"You can ground aircraft for a week, two weeks, three weeks. It would be very painful," O'Leary told Reuters in Berlin. "But we are a big company, we can survive."

O'Leary had warned last month that there were no assurances that an agreement would be in place enabling flights to continue after Britain exits the European Union next March.

O'Leary said he did not expect Ryanair to grow in Germany next year, after closing its bases in the northern city of Bremen and at Weeze near Duesseldorf.

"Our traffic will be flat," O'Leary said.

O'Leary reiterated that he was confident that Ryanair could resolve its dispute with German unions representing pilots and cabin crew. He said talks were making progress and that he did not expect further labor strikes in the coming weeks.

(This version of the story corrects to read UK flights in headline, paragraph one; corrects quote, paragraph two).

(Reporting by Klaus Lauer; writing by Maria Sheahan; editing by Thomas Seythal and Jason Neely)