How does FIFA determine nationality?

Answer 1

1. Any player who is a naturalized citizen of a country in virtue of that country's laws shall be eligible to play for a national or representative team of that country.

2. If a player has been included in a national or representative team of a country for which he is eligible to play pursuant to paragraph 1, he shall not be permitted to take part in an international match for Another Country. Accordingly, any player who is qualified to play for more than one national association (i.e. who has dual nationality) will be deemed to have committed himself to one association only when he plays his first international match in an official competition (at any level) for that association.

3. The only players exempt from this provision are those whose nationality has been changed not voluntarily but as the result of an international decree either granting independence to a region or ceding part of one country to another.