Production issues are being blamed for the delay.
Ryanair expects to be up to 10 aircraft short this summer because of ongoing Boeing delivery delays.
Boss, Mullingar's Michael O'Leary, has told the Financial Times the airline was supposed to have 57 by the end of April.
He thinks the impact will likely mean that it will now only carry 200m passengers - 5m fewer than previously forecast.
Production issues are being blamed.