Mr Abbott told Seven News he was "simply visiting a friend" after he was spotted leaving the Melbourne Assessment Prison on Monday.

Pell - who was jailed for six years for sexually assaulting two choirboys at Melbourne's St Patrick's Cathedral while he was Archbishop of Melbourne - is being held at the prison.

Former Victorian senator Derryn Hinch says the visit is a "cruel insult" to those sexually assaulted by Pell.

"For Tony Abbott, a former prime minister, to visit Pell, a convicted pedophile, is a disgrace and a cruel insult to his victims," he wrote on Twitter.

Mr Abbott phoned Pell after his guilty verdict was handed down and is one of the disgraced cardinal's many high-profile supporters.

Former prime minister John Howard wrote a character reference for Pell after he was convicted for child sex abuse.

Australia's highest court has agreed to refer Pell's case to the full bench of the High Court to hear appeal arguments.

That hearing won't be held until at least March next year..

Australian Associated Press