A preliminary study of 10 patients at the University of Oxford used a new scanning method to detect lung abnormalities not seen in conventional scans.
The technique involves patients inhaling a gas called Xenon during a magnetic resonance imaging (MRI) scan.
The research, which is led by Prof Fergus Gleeson, involved patients between the age of 19 and 69. A larger trial of up to 100 participants is now being planned, aiming to discover whether Covid-19 causes lung damage, and whether that damage is permanent.
Eight of the patients reported shortness of breath and fatigue more than three months after being ill. The scan found lung abnormalities in all of the participants which conventional scans had failed to pick up.
None of the eight patients had been admitted to intensive care or been put on ventilation machines.
Prof Gleeson is planning a larger scale trial of up to 100 people to test whether Covid-19 patients who had had the disease less severely and had not been hospitalised also show signs of lung damage.
"I was expecting some form of lung damage, but not to the degree that we have seen," he told the BBC.
The lung abnormalities could be a factor behind long Covid, where people report symptoms including fatigue long after becoming infected, the researcher said.
In the next stage of the research, Prof Gleeson plans to work with GPs to scan Covid-19 patients across a range of age groups, with the aim of discovering whether lung damage occurs regardless of age and the severity of infection.
The researcher said discovering long-term damage among younger people and those not requiring hospitalisation would “move the goalposts".
A study reported in September that up to 60,000 people in the UK have been suffering from long-Covid for more than three months.
Sufferers report a wide spectrum of health issues beyond the three NHS-approved symptoms (persistent cough, fever and loss of taste or smell). These include fatigue, breathlessness, muscle aches, joint pain, 'brain fog,' memory loss, lack of concentration and depression.
Separate data from the Covid Symptom Study app, being run by Kings College, suggests a “significant number” of people report symptoms for a month. The app, which has been downloaded more than 3,000,000 times, found that one in every 20 people experience long-term symptoms.