The family of a Qatari doctor say he has been beaten and held in solitary confinement in the UAE, after being arrested there four months ago.
Dr Mahmoud al-Jaidah was detained at Dubai Airport on 26 February.
International human rights groups have consistently criticised the UAE for detaining critics of the government.
The UAE government has said that all prisoners are treated according to the law and that any allegations of mistreatment are investigated.
Dr Jaidah has not been charged with any offence.
His case bears a striking resemblance to that of Salah Yafai who was arrested at Dubai airport on 26 April 2013.
The Bahraini citizen was held for almost seven weeks in an unknown location without charge.
Mr Yafai was released on 15 June after the Bahrain government intervened on his behalf.
Mr Yafai, a fitness trainer and educator, is a member of the Bahrain al-Islah society, a conservative religious organisation with links to the Muslim Brotherhood.
Last year 94 people, most of them members of the al-Islah society in the UAE, were arrested and are on trial charged with plotting to overthrow the government.
The detainees include two prominent human rights lawyers, as well as judges, teachers, and student leaders.
If convicted, the activists, including 13 women, each face up to 15 years in jail, with no right of appeal.