Chris Christie has checked into hospital as a “precautionary measure”, according to a tweet on his official account on Saturday.
The former New Jersey governor, who has asthma, drove himself to hospital in his home state, CNN reported.
“In consultation with my doctors, I checked myself into Morristown Medical Center this afternoon. While I am feeling good and only have mild symptoms, due to my history of asthma we decided this is an important precautionary measure,” he tweeted on Saturday.
“I am thankful for our hardworking medical professionals and look forward to coming home soon,” he added.
Mr Christie had been part of the team helping Donald Trump with debate preparation ahead of the Cleveland showdown with Democratic nominee Joe Biden earlier this week.
Several other people who were part of the prep including advisor Kellyanne Conway and senior aide Hope Hicks, along with the president himself, have since tested positive for the virus.
In a tweet on Saturday morning, Mr Christie wrote: “I just received word that I am positive for COVID-19. 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.
"I will be receiving medical attention today and will keep the necessary folks apprised of my condition.”
Mr Christie, a Trump rival during the 2016 election, told AP on Friday that the last time he was with the president was on Tuesday during preparations for his debate.
He had tweeted on Friday morning that he had last tested negative ahead of Tuesday’s debate and was not having any symptoms then.
He did not attend Mr Trump’s Bedminster fundraiser in New Jersey on Thursday.
Additional reporting by Associated Press
