Peter Saunders, who is one the members of the Holy See's Clerical Abuse Commission, was speaking before it hosted a three-day event to review the Catholic Church's safeguarding policies and the punishments in place for those who break the rules, or covered up for those who do.
Mr Saunders told The Times: "It will be outrageous if he doesn't attend and I will say so."
He also criticised the appointment of a Chilean bishop, Juan Barros, who is accused of covering up the abuse of a colleague - something Mr Barros denies.
Pope Francis has publicity backed the appointment of the bishop.
Peter Williams, a Catholic commentator, told Premier's News Hour: "I think it would behove to turn up, at least to approve what they're doing, to say 'this is good, keep on doing what you're doing', to show publicly that the Church really takes this very seriously.
"Whether or not it's a travesty if he doesn't, he's not going to be putting anything into this commission, he's wanting to listen to the commission.
"I'm hoping he will turn up just so they can say, 'okay, here are our concerns', and he can address them maybe - even if in private."
Pope Francis set up the Clerical Abuse Commission, sometimes referred to as the Vatican's special task force on safeguarding, in 2014.
He also gave new powers to the Vatican court last year, allowing them to punish bishops who fail to report the abuse of other priests.
Listen to Premier's Hannah Tooley speaking to Peter Williams on the News Hour: