Senior Catholic cleric George Pell allegedly misled a victim of sexual assault and sought to dismiss his complaint, according to documents obtained by ABC Television.
The allegation comes just days before the arrival of Pope Benedict XVI - and an expected 200,000 pilgrims - in Sydney for World Youth Day.
According to last night's ABC Lateline Program, Cardinal Pell, the head of the Catholic Church in Australia, gave misleading information to a sexual abuse victim in 2003.
The victim, Anthony Jones, claimed to have been abused by Catholic priest Terrence Goodall 20 years earlier.
In a letter obtained by the ABC, Cardinal Pell told Mr Jones the allegation had not been substantiated because the church had not received any other complaints against Father Goodall.
"No other complaint of attempted sexual assault has been received against Father Goodall," the letter allegedly said.
But another letter from Cardinal Pell, signed the same day and obtained by the ABC, was sent to a second man who also claimed to have been abused by Father Goodall.
In the second letter, Cardinal Pell told the man his complaint had been substantiated.
Mr Jones accused Cardinal Pell of getting it wrong.
"Cardinal Pell misrepresented the truth," he told ABC Television.
"I now hate Catholicism because of what Cardinal Pell has done to me, more so than what Father Goodall did to me."
Father Goodall was later convicted of indecent assault, according to the ABC.
The ABC said Cardinal Pell had not responded to a request to appear on the Lateline program or make a comment.
But Cardinal Pell has dismissed the allegations saying he had sent a letter to the victim, that was "badly worded and a mistake" and any fault in the drafting of the letter was his.
"The letter to Mr Jones was badly worded and a mistake - an attempt to inform him there was no other allegation of rape," Cardinal Pell said in a statement.
"However, I signed both letters of February 2003 mentioned in the ABC's Lateline program, and any fault in the drafting was mine.
"In a subsequent letter soon after the February 2003 letter, I expressed my sorrow at what Mr Jones had suffered and offered to meet him.
"There was no attempt to mislead him. I apologise for the confusion caused to Mr Jones."