A shortfall of seven Boeing aircraft delivered to Ryanair this summer compared to what was contractually agreed is the best possible outcome and the worst is unclear, Ryanair CEO Michael O'Leary told Reuters on Tuesday.

"At the moment we still think it's somewhere between seven and 10 but there's a risk it could be worse than that," he said in an interview, adding: "I certainly wouldn't say the worst could be 10. It could be more than that. But we've no idea." (Reporting by Francois Murphy; editing by Jason Neely)