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.
A family member said that he thought authorities in the UAE were trying to link Dr Jaidah to the 94 and to the Muslim Brotherhood.
"He is not a member of the brotherhood, a supporter maybe but not a member".
The relative said that Dr Jaidah was deprived of sleep for three days: "They beat him and made him say things he didn't do".
He added that the family did not know where Dr Jaidah was being held.
Qatar has long supported the Muslim Brotherhood, while the UAE view the brotherhood as a serious threat.
Both countries are members of the Gulf Cooperation Council (GCC).
Dr Jaidah's family told the BBC that the Qatari government had facilitated three visits, the most recent on 23 June.
On each occasion, according to the relative, the doctor was driven blindfolded to a government building in Abu Dhabi from wherever he was being held.
The family member said that Dr Jaidah told them that he was not being beaten any longer but that he was still in solitary confinement and had lost nearly two stone (10 kgs) whilst in detention.
A lawyer hired by the family had met with his client only once for 10 minutes and in the presence of an official.
The family member said "our government has told us they are trying but are getting no response. They need to try more".
No-one from the Qatari government was available for comment.