Zahir Belounis was able to finally depart Doha last week after being stranded for a year as his club Al-Jaish had refused to grant him an exit permit over a pay dispute.

Human rights organisations have repeatedly criticised the kafala sponsorship system that is applied in most Gulf countries, but with stricter conditions in Qatar and Saudi Arabia.

"Such systems make abuse and exploitation more likely," said James Lynch, researcher on migrant workers in the Gulf at Amnesty International.

People who discover recruitment agencies have deceived them about their work conditions once they arrive in the Gulf have no way to switch jobs without their sponsor's consent, Lynch said.

Qatari and Saudi conditions for exit permits give employers firm control on the movement of staff, "a tool which can be used to subject workers to serious exploitation," he added.

Belounis had to sign a settlement document before he was allowed to quit Doha for France, where he is planning to file a lawsuit against the Qatari football club, his lawyer has said.

Two other French businessmen, Jean-Pierre Maongiu and Nasser al-Awartany, remain stuck in Qatar.

But those are the only cases that have attracted media coverage, with other expatriates forced to suffer in silence.

"My little sister died in Gaza this summer, but I could not get an exit permit in time to travel to attend her funeral," said Mahmud Abdelrahim, a Palestinian who works in Saudi Arabia.

"The impact of sponsorship systems can be particularly serious for those in low-paid jobs, who face difficulties in claiming their rights via often unresponsive labour complaints systems," said Lynch.

Domestic workers "face particular risks of abuse," he said, adding that they are excluded in most Gulf countries from the "protection of labour laws, meaning that there are no legally binding standards to guarantee their living and working conditions".

Employers do not hesitate to confiscate passports of workers, withhold their salaries, and force them to work against their wishes, said Human Rights Watch.

The spotlight recently fell on Qatar when rights watchdogs raised fears over the conditions of construction workers as the emirate embarks on massive developments to prepare for the 2022 football World Cup.

The kafala system was a "modern form of slavery," charged Saudi rights activist Walid Abulkhair, insisting that "it should be abolished".

The system has also created a large market for Gulf nationals to act as sponsors and trade in visas needed by migrant workers desperate to land in the oil-rich region.

It was a core problem that triggered a massive Saudi crackdown on illegal migrants and those sponsored by Saudis who are not their actual employers. 

Bahrain is the only Gulf country that has abolished the sponsorship system, but other members of the Gulf Cooperation Council have taken measures to improve the situation of workers.

In the United Arab Emirates, employers do not have the right to ban employees from leaving the country.

Employers are also not allowed to confiscate the passports of workers, or to withhold salaries.

"A worker could even change his sponsor, but under conditions," said Mohammed al-Kaabi, a member of the UAE Association for Human Rights.

A similar system is applied in Kuwait.

"Gulf countries do not respect international labour conventions, which they have signed," charged Mohammed al-Humaidi, the head of the Kuwait Association for Human Rights.