The convener of Jatiya Oikya Prokriya and Gano Forum chief, Dr Kamal Hossain, went to Singapore for medical treatment.
He, along with his wife, left Dhaka from Hazrat Shahjalal International Airport at 2am, Wednesday on a Thai Airways flight, his family said.
Dr Kamal is supposed to return on Oct 6 or 7.
He was scheduled to go to Singapore on Tuesday which was later postponed to Wednesday night.