Ryanair has warned it will cut flights between Britain and the EU if there is no air travel agreement by September next year.
The airline's chief commercial officer David O'Brien said flights would be affected from summer 2019 onwards, the BBC reported.
He added that the company would relocate 85 aircraft from Britain to other airports in Europe.
It is not the first time bosses at Ryanair have spoken frankly about how Brexit will impact the business.
Ryanair's chief executive Michael O'Leary has said British ministers "don't have an idea" about how Brexit will impact the sector.
The firm said the ongoing uncertainty about the government's direction of travel on Brexit meant Ryanair was looking elsewhere for growth opportunities.