Chris Christie, the former governor of New Jersey who for several days this week helped the president prepare for the debate, said he has tested positive for the coronavirus.
Mr. Christie said Saturday that he would be receiving medical attention the same day.
“I just received word that I am positive for COVID-19,” Mr. Christie said on Twitter. “I want to thank all of my friends and colleagues who have reached out to ask how I was feeling in the last day or two.”
Mr. Christie was one of several advisers who huddled with President Trump and others for debate preparation from Sunday to Tuesday. Mr. Christie also attended a White House event on Sept. 26 for Judge Amy Coney Barrett in the Rose Garden.
The debate preparation team included Hope Hicks, one of Mr. Trump’s his closest advisers, Stephen Miller, the president’s speechwriter and top domestic policy adviser, and Rudolph W. Giuliani, Mr. Trump’s personal lawyer and the former mayor of New York.
None of them wore masks, Mr. Christie said.
Mr. Christie’s statement came one day after Senator Thom Tillis, Republican of North Carolina and Senator Mike Lee, Republican of Utah, announced that they had tested positive. Both attended the event for Judge Barrett. A video posted on Twitter shows Mr. Lee hugging people at the event.