Rudy Giuliani, US President Donald Trump’s campaign lawyer, has tested positive for Covid-19.
Mr Trump made the announcement on his official Twitter account on Sunday.
"Rudy Giuliani, by far the greatest mayor in the history of NYC, and who has been working tirelessly exposing the most corrupt election [by far] in the history of the USA, has tested positive for the China Virus. Get better soon Rudy, we will carry on," he said.
Mr Giuliani is 76, and therefore considered to be vulnerable.
The former mayor of New York has been one of the president's main champions in trying to overturn the election result, repeating claims of voter fraud without providing any substantive evidence.
In November, he said: "The most important thing here is that this has been a massive attack on the integrity of the voting system in the greatest democracy on Earth.
"The people who did this have committed one of the worst crimes that I have ever seen or observed."
Many of the campaign team, including the president, tested positive for the virus in October.
Mr Trump later recovered after spending a couple of days in hospital, where he was treated with the antiviral drug remdesivir, the steroid dexamethasone and the unapproved experimental antibody Regn-Cov2.
The US recorded 2,190 deaths from Covid-19 on Saturday.