More than a thousand of Ms. Yingluck’s supporters gathered in the capital hours before Friday’s hearing, but the police blocked roadways and set up barricades to prevent the crowd from getting close to the courthouse. The supporters showed up even though she had advised them not to do so.

Ms. Yingluck’s lawyer told the court that she had Meniere’s disease, which causes fluid buildup in the eardrums, and was suffering dizziness and severe headaches, but the court did not accept that as an excuse because Ms. Yingluck had not sent a doctor’s certificate. It rescheduled the verdict for Sept. 27. The court also ordered her to forfeit her bail of 30 million baht, about $900,000.

Unlike her brother, who fled the country and was convicted in absentia on corruption charges, Ms. Yingluck remained in Thailand and fought the charges against her.

Nathathorn Prousoontorn, a police lieutenant general who heads the Immigration Bureau, said that there was no record of her leaving the country since 2014. In May 2015, the court ordered her not to leave Thailand without permission.

There was widespread speculation in the Thai news media and on social media that Ms. Yingluck had gone to Dubai in the United Arab Emirates, possibly by way of Cambodia and Singapore, or to Hong Kong. Her brother has been reported to be living in Dubai.

Prime Minister Prayuth Chan-ocha and Deputy Prime Minister Prawit Wongsuwan told reporters that they had no idea where she was.

“She might be really sick. We don’t know,” Mr. Prawit said. “Maybe she is in some hospital. She is a former prime minister and some officials might have helped her if she is running away. I don’t know if she has left the country or not.”