Public Health Ministry permanent secretary Dr Sukhum Karnchanapimai announced the news on Friday (March 6).
The Briton was admitted to a private hospital on March 3 with high fever and a cough and was later transferred to an institute specialising in respiratory disorders.
A 30-year-old female migrant labourer just returned to Thailand from overseas is suspected of being infected and is undergoing tests at the Bamrasnaradura Infectious Diseases Institute in Nonthaburi.
The 48 confirmed cases in Thailand thus far break down to 16 still being treated in medical facilities, 31 recovered and one dead.