The two American World Cup Jews, previously-profiled Jonathan Bornstein and Benny Feilhaber, are subject of this thorough article. It also mentions a third, Jonathan Spector, who is at least 1/4 Jewish, grandson of former Boston Celtic Art Spector.
But we wanted to profile someone non-American for the World Cup. And Samuel was always a case where the Jewishness was not clear. This Haaretz article helped out, and it also names another famous soccer player with supposed Jewish roots: David Trezeguet of France (he's not playing in this World Cup, however).
Big thanks to reader Maxim from Israel for pointing out the latter article. Samuel was also suggested by Lee from London.