The Public Health Ministry is looking into the cause of death of a foreigner who died in Phuket on Thursday after learning he had come from Lagos, Nigeria.
The result is expected to be known on Sunday, said permanent secretary Narong Sahametapat.
The man, who reached Phuket on Oct 7, was found fainted on a beach at midday on Oct 15.
Doctors found he had a heart-disease condition and the symptoms were inconsistent with Ebola. He was therefore treated for the symptoms and sent home.
But on Thursday, police found him dead in his room and asked the ministry to help determine the cause of death.
Dr Narong said since the man flew from an Ebola-inflicted area, he would be tested for the deadly disease although first symptoms did not indicate he had been infected.
The World Health Organisation declared Nigeria free of the disease on Oct 20 after no new cases had been reported for 42 days.
In any case, the ministry applied caution by adopting Ebola protocols in handling the dead man, Dr Narong said.
It sent a fast-moving team from the Bureau of Epidemiology to join the Phuket Public Health Office in the investigation.
His room was cleaned up by the Health Department and samples of blood found there were being tested for the virus at the Department of Medical Science and King Chulalongkorn Memorial Hospital.
Sopon Mekthon, director general of the Disease Control Department, said the body was at a state hospital and the 25 people who had been in contact with the man were on a watch list.
"If the Ebola test comes negative, an autopsy will be performed," he said.
The ministry screens travellers from the affected areas in all transport modes every day.
Of all 2,415 people on the watch list to date, none has shown the symptoms.