The family of a sick Australian grandfather expresses fears that he will die in a Qatari jail where he has been imprisoned for three years after a bitter falling out with a member of the emirate's royal family.

Joseph Sarlak, 70, claims he been wrongfully imprisoned since July 2016 at the behest of his former Qatari business partner, a sheikh from the ruling Al Thani family.

Mr Sarlak's brother, Amir, said his sibling has heart problems and other health issues and begged Prime Minister Scott Morrison to intervene to help free him.

Sarlak's troubles in Doha began in 2016 after the aviation-related business he had started was accused of bouncing cheques.

Sarlak's lawyer, Radha Stirling, said her client was not responsible for the bad cheques because despite being named as a partner in the business he had no control of its day-to-day operations because of Qatari laws requiring foreigners to have a local sponsor.

The sheikh had teamed up with Sarlak in the company, but then used it as a cash cow and fleeced it of funds, Ms Stirling said.

As the company spiralled into debt, Sarlak was forced to sign a confession in Arabic and he was thrown in jail, she said.

Stirling said the cell holding Mr Sarlak, who has three children and two grandchildren, was infested with cockroaches and that he was in "chronic and serious" pain.

The criminal charges relating to the bounced cheques have been resolved, but Mr Sarlak remains in custody because he does not have a valid visa and cannot get one without a Qatari sponsor, she said.

Ms Stirling said her attempts to contact Foreign Minister Marise Payne and Australia's ambassador to Qatar had so far failed.

Stirling warned there are 3000 Australians working in Qatar who could easily find themselves vulnerable to the predicament facing Sarlak.