Tesla and SpaceX CEO Elon Musk.

Tesla and SpaceX CEO Elon Musk said on Saturday that he "most likely" has a moderate case of COVID-19, while questioning the reliability of the tests he has had. 

Asked by a Twitter user about his symptoms, he wrote that they feel "just like a regular cold, but more body achy & cloudy head than coughing/sneezing."

On Friday, he told his 40 million Twitter followers that he had "Mild sniffles & cough & slight fever past few days."

The suspected illness is likely to prevent Musk from attending a space launch on Sunday.

Four NASA astronauts are set to be launched by SpaceX on a flight to the International Space Station. NASA's health rules bar any suspected COVID-19 patient from attending, as Business Insider reported

Musk has previously expressed confusion about the test results he has had so far. 

On Thursday, he tweeted that he has had two negative and two positive tests from different labs, saying: "Something extremely bogus is going on."

But as Business Insider's Lauren Frias and Kate Duffy reported, there is nothing unusual about that situation.

Positive results in the test he appears to have taken — an antigen test — are described by the FDA as "highly accurate." But false negatives are also possible — meaning that a negative doesn't necessarily rule out the positive test.

In July, Musk wrote that testing errors were the likely cause of the surge in cases at the time, an assertion that virologist Angela Rasmussen branded "dangerous misinformation."

Receive a daily news update on your cellphone. Or get the best of our site emailed to you.

Go to the Business Insider front page for more stories.