As he sits in bed, the man can be seen responding to dozens of letters.
Eventually, the nurses give him the happy news he can finally go home after recovering from his bad bout of coronavirus.
The ad ends with the revelation the man the NHS staff have been dutifully caring for is Santa Claus.
The criticism of the ad was brutal, with some labelling it "shameful" and "disgusting".
In a statement, NHS Charities Together said the ad initially garnered an "overwhelmingly positive response" and wasn't intended for children.
"We created our Christmas campaign to highlight the ongoing commitment and hard work of NHS staff and volunteers to keep us safe and well in what has been and continues to be a really challenging time for the NHS," the charity said.
"Some people have expressed their concern about it upsetting children. The ad has been made to engage charity supporters and those who may want to buy products that generate donations to the appeal.
"It isn't aimed at children and hasn't been shown on TV. The charity did not put any funds into the production of the ad.
"We worked closely with the team behind the ad to make sure it was produced responsibly and it was cleared for use by the relevant regulatory authority.
"However, we are sorry to the parents of any young children who have been upset by watching the ad and to the young children themselves, they were not the intended audience for it."