In a message posted on her Facebook page, Nualphan said she had developed “clear symptoms” the previous night, with a high fever, sore throat and heavy cough.
“I am being treated at home. I would like to inform everyone who has been in close contact with me [about the infection],” she wrote.
She also apologised for having to cancel her appearances at public functions.
“Please stay safe and take care of yourselves,” she added.
Her Facebook post drew a tide of get-well-soon messages from netizens.
The 56-year-old is CEO of Muang Thai Insurance Plc and manager of the Thailand men’s national football team – the first woman to take the role.
She also owns the Port Football Club, along with companies that import high-end fashion brands including Hermes and Emporio Armani.
Nualphan boasts assets worth more than 4.6 billion baht, according to her declaration to the National Anti-Corruption Commission.