Austrian Cardinal Christoph Schönborn made the warning on Sunday during the church festival "Holy Name of Mary", which was first introduced 333 years ago in gratitude for the victory over the Ottomans in the Battle of Vienna.
According to the Archdiocese of Vienna, the cardinal said: "Will there be an Islamic conquest of Europe? Many Muslims want that and say: Europe is at the end."
He asked God to have mercy on Europe and to show mercy to its people, which he said "are in danger of forfeiting our Christian heritage".
Schönborn explained that people could already feel this loss, "not only economically, but above all, in human and religious matters".
The cardinal's statement came as many places across Austria commemorated the 333rd anniversary of the Battle of Vienna. During the battle on 11-12th September 1683, combined Christian forces defeated over 100,000 soldiers from the Ottoman Empire.