Ryanair boss Michael O'Leary has said a hard Brexit could ground planes for up to three weeks as the prime minister heads to Brussels for a crunch meeting with EU leaders to break the impasse in the negotiations.
O'Leary said that while the grounding of planes for a "week, two weeks, three weeks" would be "painful", the airline would survive.
O'Leary has previously warned about the dangers of a no-deal Brexit, in which the UK would crash out of the EU on terms set by the World Trade Organisation. He warned last month that the EU had given no assurances to the UK that an agreement would be in place that would allow flights to continue when Britain leaves the bloc in March 2019.
The airline has endured a turbulent summer of strikes from pilots and cabin crew over pay which drove it to issue a profit warning earlier this month.
O'Leary has said he is "hopeful and optimistic" that the issue of strikes will be resolved by Christmas.