That is not to say it is not praiseworthy to attend Orthodox Liturgies, simply that the obligation is to attend a Catholic Liturgy, if one cannot attend a Catholic Liturgy there is no obligation.
From the CCEO:
1. The Christian faithful are bound by the obligation to participate on Sundays and feast days in the Divine Liturgy, or according to the prescriptions or legitimate customs of their own Church sui iuris, in the celebration of the divine praises.
2. In order for the Christian faithful to fulfill this obligation more easily, the available time runs from the evening of the vigil until the end of the Sunday or feast day.
3. The Christian faithful are strongly recommended to receive the Divine Eucharist on these days and indeed more frequently, even daily.
4. The Christian faithful should abstain from those labors or business matters which impede the worship to be rendered to God, the joy which is proper to the Lord's day, or to the proper relaxation of mind and body.
From the CIC:
Can. 1247 On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass. Moreover, they are to abstain from those works and affairs which hinder the worship to be rendered to God, the joy proper to the Lord’s day, or the suitable relaxation of mind and body.
Can. 1248 §1. A person who assists at a Mass celebrated anywhere in a Catholic rite either on the feast day itself or in the evening of the preceding day satisfies the obligation of participating in the Mass.
§2. If participation in the eucharistic celebration becomes impossible because of the absence of a sacred minister or for another grave cause, it is strongly recommended that the faithful take part in a liturgy of the word if such a liturgy is celebrated in a parish church or other sacred place according to the prescripts of the diocesan bishop or that they devote themselves to prayer for a suitable time alone, as a family, or, as the occasion permits, in groups of families.