Air France estimates that last month's two-week pilots strike will cost it about €500m in lost revenue.
The Air France-KLM group, Europe's second-biggest airline, was already in difficulty in a fiercely competitive sector completely revolutionised by low-cost upstarts such as easyJet and Ryanair.
But finance director Pierre-Francois Riolacci told reporters that the combined impact of the 14-day strike and the loss of future custom from disgruntled passengers would be "in the order of 500 million euros" ($632 million).
"We need a few more days to finalise completely our estimates. But we think the impact on the third quarter will be in a range of 320-350 million euros," Riolacci said.
Pilots at Air France waged the record-long strike between September 15 and 28 in protest at the group's plans to expand its low-cost subsidiary Transavia France.
The airline, which is 16-percent state-backed, sees the development of Transavia France as crucial to compete in the cut-throat world of aviation, particularly on short-distance routes in its home market.
But in a concession to end the strike, Air France management abandoned a strategy to expand Transavia into Europe.