The family of a British-Australian man jailed in Mongolia over a soured business deal fear he will not survive his seven-year prison sentence, after the country’s supreme court upheld his controversial conviction.

After a trial last July that lasted just two days, Mohammed Ibrahim “Mo” Munshi was jailed and fined $15m over a coal deal struck between Gobi Coal and Energy, of which he was chairman, and a company owned by Chuluunbaatar Baz, a member of a prominent Mongolian family.

Munshi is the latest in a string of foreign investors to find themselves hit with arbitrary travel bans or prosecuted over business deals in resource-rich Mongolia, as local partners seek to seize assets or alter agreements.

Last month, Mongolia’s supreme court upheld his conviction, while reducing his original 11-year sentence to seven years on a technicality.

Munshi’s only hope for earlier release lies with an international arbitration application – a process that could take several months – or with a complaint to the United Nations human rights council alleging he was denied a fair trial.

Munshi’s son, Arif, told the Guardian from Perth, where Munshi’s children and elderly parents live, that they fear he will not survive a long prison sentence, particularly during Mongolia’s harsh winters. Munshi has already been hospitalised and the medications he requires regularly run out.

“Honestly, I fear for my father’s life,” Arif Munshi said. “He has several serious health concerns which are not being adequately treated. If the Mongolian authorities cannot provide the medications they saw fit to prescribe him, what hope does he have of maintaining his health?

“In the closed prison, he is housed with dangerous criminals including rapists and murderers. He lives in constant fear for his safety and his life.”

Arif Munshi has said he has been “disillusioned and disappointed” by the diplomatic efforts of the Australian government to assist his father.

He said he had understood that while his father’s trial and appeals processing were ongoing, governments were reluctant to intervene in, or publicly pressure, the judicial processes of a foreign country.

“But we are now at the end of the legal process and we are asking what can the Australian and British governments do?

“Given the lack of evidence and the total disregard shown by the Mongolian legal system for its own laws, is the Australian government going to do something to help? Can the Australian government honestly say that my father has been given a fair trial, or even a fair go?”

A spokeswoman for the Department of Foreign Affairs and Trade said the government was “providing consular assistance to a dual UK-Australian national serving a prison sentence in Mongolia, in accordance with the Consular Services Charter”.

Munshi’s Australian lawyer, Alisdair Putt, a former commonwealth and state prosecutor, and investigator in the International Criminal Court prosecutor’s office, said he does not believe Munshi received a fair trial or appeals process.

“There was minimal evidence presented at trial that could result in a conviction ... this matter should have been treated as a commercial dispute between two companies.”

Munshi’s dispute arose after Baz’s company, Monnis International, invested $10m in Gobi Coal’s proposed mining projects in the south-west of the country.

But when the global coal price collapsed in 2012, a proposed initial public offering was postponed, with the projects put on hold until prices recovered. Other investors acceded to ride out the price dip, but Baz reportedly demanded his money back.

Attempts at arbitration failed, and when Munshi visited Mongolia in 2015 he was hit with a travel ban and his passports were confiscated. The dispute dragged on until mid-2017, when Munshi was arrested, tried, convicted in a two-day trial and jailed. Gobi Coal’s licence over coal deposits was also suspended.

In court documents from the trial, Baz alleged he had been tricked into investing in the projects and defrauded of his investment.

Munshi has denied the allegations and said the case was a business dispute that should be settled by international arbitration, not by punitive use of the criminal justice system.

Court documents state that Baz repeatedly offered to abandon the criminal prosecution in exchange for some of his investment being returned.

Attempts by the Guardian to contact Baz have not been returned.

Both the Australian and UK governments have highlighted the use of travel bans as a tactic to settle commercial disputes in Mongolia, while the US state department has warned: “Investors and local legal experts have grown to fear what they call the capricious and arbitrary use of travel bans by Mongolian officials, sometimes at the behest of private interests, as a means to coerce foreign investors to settle civil and criminal disputes.”