When the Reformation began to take hold, the Orthodox may have been in decline, but were definately still present. I'm curious to know what what the two "breakaways" thought of each other - is it a case of "my enemies' enemy is my friend," or was the doctrinal difference too great?
I linked to this article in another question, but it's certainly relevant here:
Some Lutherans did make contact with Patriarch Jeremias II of Constantinople. They gave him a copy of the Augsburg Confession and requested his reaction. The Patriarch politely thanked them and, later, gave a detailed reply, indicating where the various points of the Lutheran document were in conflict with Orthodox doctrine.
The Reformers, in turn, composed a detailed reply to explain themselves and assert that doctrinally the two churches were not really so far apart. The Patriarch replied at greater length, again explaining which doctrines were not acceptable to the Orthodox faith.
The Reformers sent one more letter, but the Patriarch felt things were at an impasse. He replied requesting no more correspondence on matters of doctrine, but rather "for the sake of friendship."