Seven Greek islands were removed from the safe list earlier, meaning travellers arriving back in the UK will be expected to self-isolate for 14-days from tomorrow.
The low-cost carrier said customer confidence to make travel plans had been “negatively affected” by the changes.
easyJet said it now expects to fly “slightly less” than the 40 per cent of planned capacity in the fourth quarter of 2020.
Johan Lundgren, chief executive of easyJet, explained: “As we said at our quarter three trading update, we are closely monitoring customer behaviour and amending flying to ensure our schedule is aligned with demand.
“Following the imposition of additional quarantine restrictions to seven Greek Islands and the continued uncertainty this brings for customers, demand is now likely to be further impacted and therefore lower than previously anticipated.
“We will continue to take a prudent and conservative approach to capacity, as we have done during this period.”
easyJet said, given the many changes to government restrictions since the most recent update, the lack of visibility and the continued level of uncertainty, it was also unable to provide financial guidance for this year and next.
The carrier added it would continue to focus on delivering a flying schedule that drives a positive contribution while maintaining focus on minimising cash burn.
Lundgren joined with voices from across the hospitality industry in demanding a more predictable quarantine regime.
He added: “We called on the government to opt for a targeted, regionalised and more predictable and structured system of quarantine many weeks ago so customers could make travel plans with confidence.
“It is difficult to overstate the impact that the pandemic and associated government policies have had on the whole industry.
“We again call on the government to provide sector specific support for aviation which needs to take the form of a broad package of measures including the removal of air passenger duty for at least 12 months, the alleviation of air traffic control charges along with continuation of the slot rule waiver.”