After two lost appeals at the Court of Arbitration for Sport, Munir El Haddadi was cleared Friday to represent Morocco in international soccer.
FIFA confirmed the transfer from Spain was made possible by slightly amending rules passed in September to govern requests by players with dual nationality to change eligibility.
FIFA did not immediately respond to a request to explain why the amendment was made.
Munir can now be selected by Morocco next month for African Cup of Nations qualifying games, and later for World Cup qualifying.
Morocco wanted Munir on its team at the 2018 World Cup but the Sevilla forward's first application to FIFA was rejected and upheld by CAS because he played one competitive game for Spain in 2014. Munir, then a teenager with Barcelona, made a brief appearance as a substitute in a European Championship qualifier.
The second application to FIFA was rejected in October, and also later confirmed by CAS, because of a technicality in the new rules. Munir had played for Spains under-21 team in a competitive game after he turned 21 in September 2016.
Now, a FIFA amendment means the age limit of 21 only applies to games played after September 2020, when the new rules took effect.
FIFA explained in guidance to the rule book that, in cases like Munir's, players could not have reasonably expected prior to last September that the eligibility rules would eventually be relaxed.
Morocco is leading its African Cup qualifying group with two matches to go. The north African nation will begin its World Cup qualifying program in May in a group with Guinea, Guinea-Bissau and Sudan.