Australian filmmaker James Ricketson will stand trial this Friday, facing espionage charges that carry a possible 10-year prison sentence.

Key points: Mr Ricketson says he will request the trial be postponed until he's "had an opportunity to formulate a defence"

Mr Ricketson says he will request the trial be postponed until he's "had an opportunity to formulate a defence" Mr Ricketson is currently in the prison's infirmary

Mr Ricketson is currently in the prison's infirmary He's denied the espionage accusation and says he still has not been told who he is meant to have been spying for

Mr Ricketson has been held in pre-trial detention since his arrest in Phnom Penh more than a year ago, waiting for a judge to conduct a preliminary investigation.

Judge Pich Vichearthor could have dropped the charges but has decided to go ahead with a trial.

Mr Ricketson told the ABC he expects to receive a translated explanation today of why the case is going ahead.

"Even if the judge's statement does contain evidence, two days to form a defence, call witnesses and so on, is clearly insufficient," Mr Ricketson said.

"I will be requesting that my trial be postponed until I have had an opportunity to formulate a defence."

The 69-year old is currently in the prison infirmary, suffering from a chest problem and various skin issues.

Before that he was sharing a cell with 126 inmates, with limited sanitation and constant cigarette smoke.

His son Jesse recently spoke to the ABC's 7.30 program about the cramped conditions and lack of medical treatment inside the prison.

"Worst case scenario is he could die in there," Jesse Ricketson said.

"My father's health is not good … he's squished into a tiny cell with a lot of people."

Sorry, this video has expired Jesse Ricketson is concerned about the health of his father, James Ricketson, who is in a Cambodian prison.

James Ricketson has been visiting Cambodia for more than two decades, filming documentaries such as Chanti's World and providing humanitarian assistance to impoverished families.

But he has also been highly opinionated about Cambodian politics and appears to have been caught in the middle of a crackdown by authoritarian Prime Minister Hun Sen.

Cambodia goes to the polls on 29 July and Hun Sen — who has ruled for 33 years — has threatened civil war if his party is defeated.

The former Khmer Rouge fighter ordered the main opposition party to be dissolved last year and its leader Kem Sokha detained on treason charges — effectively guaranteeing the ruling party victory in an election contested only by micro-parties.

Mr Ricketson was arrested a day after flying a drone above an opposition rally in Phnom Penh in June last year, but the investigation has focussed on seemingly-innocuous emails to the now-banned Cambodian National Rescue Party.

Mr Ricketson denies the espionage accusation and says he still has not been told who he is meant to have been spying for.

"It is unclear at this point if the Australian Embassy, the media, my family and the public will be permitted to observe the court proceedings," Mr Ricketson wrote.

"I suspect not, given the lack of evidence."