18.104.22.168 Catholics as Godparents at Baptism in a Non- Catholic Eastern Church
1. Although Catholics may serve as godparents at a non-Catholic Eastern (Orthodox) baptism, they are to be advised to decline when the person presented for baptism has already received valid baptism, or is the child of Catholic parents who is handed over to a non-Catholic religion. 
 CC. 1366 and 845 §1, Ecumenical Directory, n. 98.