Net losses are now expected to be between £689m and £732m, compared with previous guidance of between £732m and £818m, the airline said.
No reason for the revision was given.
Bosses also said Easter travel restrictions and the slow rollout of the Covid-19 vaccines saw a delay in passenger numbers recovering.
As a result of delays to international travel resuming, bosses explained they do not expect traffic to fully recover this financial year, with expected passenger numbers to be at the lower end of previous guidance between 80 million and 120 million.
Passenger numbers fell to just 27.5 million in the year to March 31, compared with 149 million a year earlier.
Ryanair said: "Easter travel restrictions/lockdowns and a delayed traffic recovery into the peak (summer) season, due to the slow rollout in the EU of Covid-19 vaccines, means that traffic is likely to be towards the lower end of our previously guided range".
It added: "While it is not possible (at this time) to provide meaningful (2021/22) profit guidance, we do not share the recent optimism of certain analysts as we believe that the outcome for (2021/22) is currently close to break-even."
The update comes days after bosses from leading airlines urged Prime Minister Boris Johnson to give them the green light for international travel within weeks.
The chief executives of British Airways, easyJet, Jet2.com, Loganair, Ryanair, Tui and Virgin Atlantic, as well as trade body Airlines UK, wrote the letter as ministers made it clear the ban on foreign travel will be in place until at least May 17.
When it is lifted it will be replaced by a risk-based "traffic light" system, with red, amber and green ratings for countries around the world.
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