In Ecumenism. The True Story of a War That Never Was , the Italian journalist Sandro Magister reports that “The patriarchs of Moscow and Constantinople threatened a complete break with Rome in 2003. The pretext was Ukraine. But at the Vatican, Kasper and Ratzinger defused the danger.”
For more on Catholic-Orthodox relations in Ukraine, see George Weigel’s “On the Square” article Storm Clouds in Ukraine . For something on Russian Orthodoxy, see David Goldman’s “First Thoughts” post Russia, Europes Most Christian Country? , which is still getting comments.