On the quantity defecting in the Great Apostasy?

On p. 230 of Fr. F. W. Faber's [*The Precious Blood*](https://ia802601.us.archive.org/21/items/a5807812fabe00uoft/a5807812fabe00uoft.pdf) , we find the words: >In the days of Antichrist, when two-thirds even of the faithful shall fall away from the Church. Now, "a revolt" is spoken about in [2 Thess. 2:3](https://www.drbo.org/chapter/60002.htm) , which, I surmise, is what Fr. Faber is referring to. Can someone shed some light as to where the "two-thirds" figure may have come from? Can it be biblically inferred?