Mr O'Leary said some pilots had been offered a 10,000-euro pay rise in exchange for helping out.
The carrier had offered pilots bonus payments of up to €12,000 to forgo their holiday entitlements.
He dismissed talk of possible industrial action, including reported plans for a work-to-rule, saying: "There isn't a union".
The antitrust probe will also look at the information Ryanair provided to customers regarding cancellations, refunds, and other solutions, and whether customers were misled regarding their right to compensation. Compensation and lost fares for the cancelled flights will cost €25m ($30m).
Ryanair reportedly plans to recruit more than 100 new pilots within the next two weeks as Europe's largest low-priced airline battles to limit the damage of mass cancellations across its sprawling fleet.
O'Leary told Ryanair's Annual General Meeting that it did not have sufficient spare pilots for September, October and November to ensure smooth operations and was considering forcing some pilots to change their annual leave plans.
Last gasp for the Republican health care effort
Meanwhile, SPDR S&P Pharmaceuticals ( XPH ) and First Trust Health Care AlphaDEX ( FXH ) declined more than 1% apiece. Kimmel himself shared a Jennifer Rubin editorial on Monday which argued that Graham-Cassidy did not pass the "test".
He added the company does not need the agreement of pilots to take back a week of leave and added that if pilots "misbehave there will be no goodies".
Ryanair estimates that the total cost will be as much as 25 million euros ($30 million) for the cancellations, which were sparked by the over-allocation of pilots' holidays during a relatively busy period.
"If Norwegian Air are holding open days, there's nothing we can do, despite the fact that we have very good terms and conditions".
They seem to have found that voice.
The pilots also say the details around the offer are too vague, particularly with regards to the number of days off pilots who accept the bonus would have to give up in order to qualify for it. But a group of pilots rejected that offer on Thursday and threatened to launch a "work to rule" campaign.
The airline announced last week that it would be cancelling up to 50 flights a day to help it reach its punctuality target for the year, sparking travel chaos across Europe.
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