Ryanair trimmed its full-year profit forecast by 5 percent Tuesday because of the fall in the value of sterling and said that average fares could drop by up to 15 percent this winter. Ryanair earns about a third of its revenues in sterling while about 20 percent of its costs are in the currency, a company spokesman said. The low-cost airline, Europe's largest, said it expects net profit for the year to March 31 of between 1.3 billion euros ($1.46 billion) and 1.35 billion euros, down from a previous forecast of 1.375 billion euros to 1.425 billion euros. The mean forecast of 16 analysts polled by Reuters ahead of the profit warning was 1.383 billion euros.

"The primary cause of this slightly lower growth in full-year profitability is the 18 percent fall of sterling post-Brexit, which will reduce second-half average fares by between 13 percent and 15 percent," Chief Executive Michael O'Leary said in a statement.

"We would caution that this revised guidance remains heavily dependent upon no further weakness in second-half fares or sterling from its current levels," O'Leary added.

Rival easyJet, half of the passengers of which originate in the UK, has already cut its profit forecast for the year to Sept. 30 in the wake of Britain's vote to leave the European Union and the subsequent fall in sterling.