One of the men who accused Cardinal George Pell - Australia's most senior Catholic – of child sex assault has died, in a development that could weaken the criminal case against the cardinal.

Damian Dignan, who lived in Ballarat in the state of Victoria, died after a long illness, less than two years after publicly alleging he was assaulted by Pell.

In an explosive television interview, Mr Dignan and another alleged victim accused Pell of touching his genitals at a swimming pool in Ballarat.

Following the interview, police confirmed they were investigating Pell, who was then one of the most powerful figures in the Vatican.

Pell, 76, was charged last June with multiple historic sex offences and is due to face a committal hearing in March. He left his post at the Vatican, where he was effectively the treasurer, to fight the charges.

Experts said the death of Mr Dignan could affect the criminal case against Pell and may require prosecutors to rethink their approach.

“It’s not an unreasonable quote to say that prosecutors could have a more difficult task now, yes,” Nicholas Papas, a former chief magistrate and crown prosecutor, told The Australian.

“Normally it requires that the person who has given evidence to be there, and so normally it would be the case that without them there, the prosecution can’t proceed ... but you can’t be absolutely sure.”