Last month, chief financial officer (CFO) Howard Millar said he would leave at the end of the year. He is also a deputy chief executive.
Mr Millar (52) is seeking a new job as a chief executive before he gets too old to take on such a new role. Both Mr Millar and Mr Cawley are remaining on the Ryanair board.
Mr O'Leary conceded that he tried to get Mr Millar to remain in a full-time role.
"He's done the CFO job now for more than 20 years. We can't offer him much more here that's exciting unless there's going to be a vacancy at the CEO level, and certainly for the next three to five years there doesn't appear to be one here."