Charles Beard: "Martin Luther:" Ch. 8--Luther and Latin Theology, 378ff.

9. Luther and the Theology of Rome, 379-405. By 1520, Luther is productive, literarily: Address to the Christian Nobility of the German Nation, Prelude concerning the Babylonian Captivity of the Church, and the little treatise, Of the Freedom of a Christian Man. Luther proceeded through stages, realizing the earlier reformers, Councils (Pisa, Constance, Basel), and Princes had failed over the decades and last few centuries. Avignon was nothing to write home about. In 1545, Trent was an acknowledgement that new and fresh foundations needed to be laid. Rome was the visible church—Bohemians and Greeks were heretics. The sacraments were the sovereign channels by which God worked. Primus inter pares gave way to Petrine supremacy. The Renaissance Papacy was corrupted—indisputable and stated by insiders also, not just Reformers. 

By 1520, one gets a cryptic note by Morice and Cranmer that the upsets over religion compelled Cranmer to study the Bible itself very closely, but attendant comments historically. Details are lacking. As a Doctor, Examiner, and Lecturer at Cambridge (by 1523 or 1526, take a pick?), presumably with a license to read Continental heretics like Luther, what was Dr. Cranmer reading and when? So far, details are missing. By 1521, however, Henry is hurling thunderbolts at Luther with approval from the Lil' Man of Rome.