The concerns contrast with Trump's own take on his condition, as he earlier claimed that he was feeling well and mused on whether he was "immune" to the virus.
In a 90-second long video message posted online a short time later, Trump said:
"I just left Walter Reed Medical Centre, and it's really something very special. The doctors, the nurses, the first responders. And I learned so much about coronavirus," he said.
"And one thing that's for certain. Don't let it dominate you. Don't be afraid of it. You're going to beat it. We have the best medical equipment, we have the best medicines, all developed recently. And you're going to beat it.
"I went, I didn't feel so good. And two days ago - I could have left two days ago. Two days ago I felt great, like, better than I've felt in a long time. As I said just recently, better than 20 years ago.
"Don't let it dominate. Don't let it take over your lives. Don't let that happen. We have the greatest country in the world. We're going back, we're going back to work. We're going to be out front.
"As your leader, I had to do that. I knew there's danger to it, but I had to do it. I stood out front, I led. Nobody that's a leader would not do what I did. And I know there's a risk, there's a danger, but that's okay.
Trump also speculated that he may now be "immune" to the killer virus.
"But now I'm better, and maybe I'm immune. But don't let it dominate your lives. Get out there, be careful. We have the best medicines in the world.
"The vaccines are coming momentarily. Thank you very much."
After filming the message Trump entered the White House, where the reach of the outbreak that has infected the highest levels of the US Government is still being uncovered.
Still Trump indicated he won't be kept from campaigning for long, tweeting before leaving the hospital, "Will be back on the Campaign Trail soon!!!"
Trump made a point of sounding confident earlier. He tweeted, "I will be leaving the great Walter Reed Medical Center today at 6.30pm. Feeling really good! Don't be afraid of Covid. Don't let it dominate your life ... I feel better than I did 20 years ago!"
Trump's nonchalant message about not fearing the virus comes as his own Administration has encouraged Americans to be very careful and take precautions to avoid contracting and spreading the disease as cases continue to spike across the country.
- Additional reporting, AP
