It follows a similar profits downgrade earlier this month from Irish no-frills airline Ryanair, highlighting the impact of Britain's sliding currency on companies that report in euros.
International Airlines Group, owner of BA and Spanish carrier Iberia, said it expects full-year operating profit of 2.5 billion euros (USD 2.7 billion), or 7.0 per cent higher compared with 2015.
That was less than an estimate provided by IAG in July for a rise of more than 10 per cent, which had also been a downgrade.
This has particularly hit IAG since tickets for its main carrier BA are mostly sold in pounds.
"Foreign exchange is becoming a material headwind, mainly on the translation of sterling profits at British Airways, and recent exchange rate moves suggest this challenge will continue to grow," broker Liberum said in a note to clients.
IAG chief executive Willie Walsh today said that the group's third quarter was affected by "a very significant negative currency impact of 162 million euros, primarily due to sterling weakness, and continued disruption due to air traffic control strikes".
IAG shares were up 2.9 per cent at 425.6 pence in morning deals on London's benchmark FTSE 100 index, which was down 0.7 percent overall.
"The fall in sterling since the Brexit vote had a significant impact on the group... Despite this, operating and after-tax profits rose and the interim dividend is up 10 percent," said AJ Bell Investment Director Russ Mould.
Ryanair recently cut its full-year profits forecast by five percent, while EasyJet warned that annual earnings would slump by almost a third on Brexit, industrial action and unrest in Egypt and Turkey.
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