Ryanair released mixed financial results in the first half of its key summer period.
Europe's largest low-cost carrier reported post-tax profit down 21% year on year at 243 million euros.
Fares fell 6% from the same period last year in a trend the company said would continue until the end of the summer - the period in which it makes all of its profits.
The key drivers were price competition in several markets including Germany and reduced spending by British consumers as the country prepares to leave the European Union on Oct. 31.
The company's chief executive Michael O'Leary said: "An obvious one (to cut) if there is a hard Brexit at the end of October, we have three UK domestic routes... They would readily fall out straight away. There is a longer-term question mark over those in a hard Brexit."
Ryanair is facing another question - over further slippage in the return to service of Boeing's grounded 737 MAX.
The company is one of the largest customers for the jet. This month it cut the number of 737 MAX jets it plans to fly next summer from 58 to 30, halving passenger growth for the year to 5 million passengers.
Ryanair boss Michael O'Leary has warned that the airline will not rule out making job cuts if the return to service of the Boeing 737 Max plane is delayed further.