President Trump tested positive for coronavirus after Hope Hicks, a close aide to the President, also tested positive for COVID-19 on Thursday.
He tweeted: “Hope Hicks, who has been working so hard without even taking a small break, has just tested positive for Covid 19. Terrible!
“The First Lady and I are waiting for our test results. In the meantime, we will begin our quarantine process!”
Ms Hicks travelled alongside President Trump on Air Force to Wednesday’s debate in Ohio.
President Trump’s physician Sean Conley has confirmed in a statement the President and his wife “are both well at this time, and they plan to remain at home within the White House during their convalescence.”
He said: “Rest assured I expect the president to continue carrying out his duties without disruption while recovering, and I will keep you updated on any future developments.”
The news has raised concerns about the health of his 77-year-old Democrat rival, Mr Biden.
The two are scheduled to clash again in Miami, Florida, on October 15.
And the election itself is scheduled to take place on Tuesday, November 3.
“The failure of the Trump administration to take the coronavirus seriously put Joe Biden and countless others in harms way.”
He then said in another tweet: “Joe Biden cancelled all of his in-person fundraisers at the first sign of the virus.
“Donald Trump travelled to a fundraiser after he knew he had been exposed. Tells you all you need to know.”
Because of their age, both President Trump, 74, and Mr Biden, 77, are considered at risk from COVID-19.
According to the US Centers for Disease Control and Prevention (CDC), older adults and people with medical conditions are most at risk of severe illness.
The CDC said: “As you get older, your risk for severe illness from COVID-19 increases.
“For example, people in their 50s are at higher risk for severe illness than people in their 40s.
“Similarly, people in their 60s or 70s are, in general, at higher risk for severe illness than people in their 50s.
“The greatest risk for severe illness from COVID-19 is among those aged 85 or older.”
The Wednesday debate was organised according to social distancing rules to minimise the threat of the virus spreading.
The event was held at the Cleveland Clinic health centre and anyone entering the hall was screened by having their temperatures measured.
And throughout the campaign trail, Mr Biden appears to have taken all the necessary precautions to minimise the risk of contracting COVID-19.
He has been seen wearing face masks when in public outings and has met with supporters in small, socially distance groups.
In stark contrast, his rival has openly mocked Mr Biden for wearing face masks, stating he would likely not wear one.
He said in April: “I don’t think I’m going to be doing it. Wearing a face mask as I greet presidents, prime ministers, dictators, kings, queens – I just don’t see it.”
President Trump has also been hosting large rallies with his supporters, going against health and safety guidelines concerning coronavirus.