Dr Hilary Jones has issued a stark warning of a "very concerning" side-effect of the coronavirus.
The Good Morning Britain doc, 67, said some patients may develop a brain fog months after recovering from the deadly bug.
The telly doctor said those who do experience the side-effect will be faced with a "crippling" inability to think clearly.
He said the brain fog may even affect people from going about their day-to-day activities.
Speaking about a new study led by Imperial College London, Dr Hilary issued the warning to viewers at home.
The study - consisting of questionnaires answers from 85,000 coronavirus patients - left many concerned with the issues regarding long-term cognitive impact the brain suffers after microbleeds or strokes.
The study's lead author Adam Hampshire said brain fog was developed in patients who had coped with the virus at home and received no hospital treatment.
A former Covid-19 patient who now experiences brain fog symptoms, told The Guardian : "Brain fog seems like such an inferior description of what is actually going on. It’s completely crippling. I am unable to think clearly enough to do anything,
"I can’t work more than one to two hours a day and even just leaving the house to get some shopping can be a challenge."
She added: “It often prevents me from being able to have a coherent conversation or write a text message or email. I feel like a shadow of my former self. I am not living right now, I am simply existing.”
It comes as Dr Hilary issued yet another warning over a reliance on herd immunity amid the pandemic.
He addressed new concerns about a Covid-19 vaccine, and whether one will be ready by Christmas as it has previously been hoped - while there is also uncertainty over what immunity a vaccine may offer.
Hilary urged people to follow the government guidelines, whether or not they had had the virus.
There's now uncertainty again over herd immunity and coronavirus antibodies, and whether these give someone immunity for long enough.
With antibodies now shown to disappear quite quickly in the more vulnerable groups after time, Hilary warned that group immunity could be "way, way off".
* Good Morning Britain airs weekdays at 6am on ITV.
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