Grange University Hospital said it was under ‘significant pressure’ because of the number of coronavirus patients being hospitalised.
Ted Edwards’ family said they had to wait until the next day for updates on the 73-year-old.
Mr Edwards was ill on Friday night and put in an ambulance on Saturday where he was left for hours overnight.
His niece, Poppy Vaughan Winter, said the family were still waiting for updates on Sunday morning.
On Saturday she said: ‘We’ve just been told his condition’s not changed, but he is still waiting in the ambulance.’
On the same day the Aneurin Bevan University Health Board, which runs the hospital in Cwmbran, South Wales, said: ‘The Grange University Hospital is under significant pressure this afternoon due to the very high number of Covid-19 patients presenting.
‘We’re now struggling to identify beds for our patients and we also have a high number of ambulances waiting outside the hospital.
‘This is a very serious situation and we are experiencing this demand on our services before we see the normal increase in demand as the result of cold weather and flu in the winter.’
Bob Tooby, from the Welsh Ambulance Service, said: ‘We now have over 1,900 Covid-19 patients at hospitals across Wales.
‘This has included some long delays with patients on our ambulances, but it would not be appropriate for the patients or indeed their families for us to provide the specific details at this time.’
The number of coronavirus patients admitted to hospitals in Wales has been rising since the end of September, according to official government data.
The beginning of December had 1,171 people in Welsh hospitals for coronavirus which rose to 1,231 in just eight days.
It always seems impossible until it is done.