A human rights group is calling on Abu Dhabi to take urgent action against the head of state's brother after video emerged of him torturing another man.
Human Rights Watch called for a full investigation into Issa bin Zayed al-Nahyan over the footage.
The United Arab Emirates Interior Ministry confirmed that the 45-minute video featured Sheikh Issa, but said the issue had been resolved privately.
The victim is seen being beaten, given electric shocks and crushed by a car.
A man in police uniform and several other men are seen assisting the sheikh in the abuse, as the terrified victim is held down in the sand.
The UAE says a police investigation found no breach of its rules in the incident.
A former business associate of Sheikh Issa al-Nahyan says he smuggled the video out of the UAE.
Bassam Nabulsi, who is suing the sheikh in a US federal court, gave a copy of the tape to the US television network ABC which broadcast clips, saying parts of it were too graphic to be shown.
The footage shows bullets being fired near Afghan businessman Mohammed Shah Poor as he lies tied up screaming on the desert floor. Sand is shovelled into his mouth.
He is also struck repeatedly with a plank with a protruding nail, and had salt rubbed into his wounds.
In the unbroadcast footage, an electric cattle prod reportedly is used on the private parts of the victim, who had been accused of cheating the sheikh in a business deal over a consignment of wheat.
Near the end of the tape, Poor is made to lie onto the ground and the sheikh drives over him repeatedly, with the sound of what appears to be breaking bones audible on the tape.
Human Rights Watch described the acts on the tape as a violation of the UAE's constitution and international law.
"The government's failure to prosecute those involved in this undisputed incident of torture and abuse at the hands of a royal family member and the police is an appalling miscarriage of justice," said HRW's Sarah Leah Watson.
It said the apparent involvement of a police officer was "tantamount to state complicity in the torture".
The UAE said the police investigated the events, and found that "all rules, policies and procedures were followed correctly by the Police Department", according to a letter seen by Human Rights Watch.