The survey of 1,002 people, conducted by market research company Censuswide in October for recruitment website Indeed, adds to signs that long COVID continues to be a factor behind widespread labour shortages in Britain.
Some 98% of long COVID sufferers said the condition had limited their ability to work, 78% had needed to cut back or change their work and 19% had ceased work altogether.
Long COVID, a collection of symptoms ranging from pain and heart palpitations to insomnia and brain fog, can last for many months after initial infection.
Of those, 73% said long COVID was limiting their day-to-day activities, and 16% - 333,000 people - said their activities had been significantly limited.
In the Indeed survey, 59% of people diagnosed with long COVID said they felt more tired, 42% felt physically weaker, 37% found it harder to concentrate and 19% were in pain when working.