The Benfica player was handed the ban by UEFA following accusations he directed a slur at Real Madrid's Vinicius Jr during February's Champions League playoff clash, which Real won 1-0.
"The FIFA Disciplinary Committee has decided to extend the six-match ban imposed by UEFA on SL Benfica player Gianluca Prestianni to have worldwide effect," a FIFA spokesperson told Reuters.
"The sanction has been extended in accordance with article 70 of the FIFA Disciplinary Code."
The worldwide extension, which was requested by UEFA, means Prestianni would miss Argentina's first two World Cup fixtures if he is selected.
The ban covers UEFA club competition games or competitive international matches, but not friendlies or domestic league games.
UEFA originally imposed the six-match suspension for discriminatory conduct, with three games suspended for a probationary period. Prestianni had already served a one-match provisional suspension when he missed the second leg against Real Madrid.
The 20-year-old has limited international experience, however, making just one appearance for Argentina as a late substitute in a November friendly against Angola.
Argentina open their World Cup campaign on June 16 against Group J opponents Algeria before taking on Austria and Jordan.
