Vatican finance chief George Pell was on Monday called to give evidence at an inquiry into sex abuse as one of Pope Francis' commissioners for the protection of children accused him of being "almost sociopathic".

Formerly the top Catholic cleric in Australia, Cardinal Pell has become embroiled in the probe in his homeland which last week heard evidence from paedophile priest Gerald Ridsdale, who abused at least 50 boys over two decades.

Pell, who accompanied Ridsdale to court in 1993 when he admitted widespread abuse, has repeatedly denied knowing about any of the offences, helping move the priest to another parish or that he tried to bribe a victim to keep him quiet.

That victim was his nephew, David Ridsdale, who alleged he confided in family friend Pell about the assaults and that he was asked by him what it would cost to buy his silence.