FYI
Canon 844 states: “It is lawful for the [Catholic] faithful for whom it is physically or morally impossible to approach a Catholic minister, to receive the sacraments of penance, Eucharist, and anointing of the sick from non-Catholic ministers in whose churches these sacraments are valid” (Ibid.). Since the Catholic Church recognizes the validity of the Orthodox Eucharist, a Catholic may, in case of necessity, receive Communion in an Orthodox church.
But (with a capital B), the Orthodox churches generally do not allow Catholics (or members of any other denomination) to receive communion in their churches. So for a Catholic to ignore such a prohibition would be to show disrespect for Orthodox regulations. By the same token, Orthodox are generally not allowed by their own leadership to receive communion in a Catholic (or any other) Church.
On the matter of Catholic-Orthodox intercommunion, the U.S. Catholic bishops summed up the matter nicely in their November 1996 Guidelines for the Reception of Communion at a Catholic Mass: “Members of the Orthodox Churches, the Assyrian Church of the East, and the Polish National Catholic Church are urged to respect the discipline of their own Churches. According to Roman Catholic discipline, the Code of Canon Law does not object to the reception of communion by Christians of these Churches.”
Thank you for that clarification, STF.