The former Pope John Paul II will be beatified tomorrow in a ceremony at the Vatican.

Beatification, in which a person is declared “blessed,” is a necessary prelude to canonization as a saint. Under the rules of the Catholic Church, for a person to be beatified he must be proven to have performed a miracle.

In John Paul II’s case, a French nun named Sister Marie Simon-Pierre Normand claimed that she and her fellow nuns -- the Congregation of Little Sisters of Catholic Maternity Wards based in Puyricard, near Aix-en-Provence -- prayed for the intercession of the pope after his death in order to cure her of Parkinson's Disease.

She was indeed “cured” and she later continued to work as a maternity nurse, according to the Vatican.

The Congregation for the Causes of Saints said doctors appointed by the Holy See scrupulously studied her case and determined her cure had no medical or scientific explanation.

However, Sister Marie has reportedly again become ill again since her recovery and now there are concerns that Parkinson's Disease diagnosis might have been incorrect.

Thus, if it emerges that she was not the recipient of a miracle, John Paul’s sainthood would be blocked.

Read More: Massive crowds gather for Pope John Paul II beatification [PHOTOS]