USSR was a top-4 football nation in the 1st half of 60s (see titles, WCs games & ELO ratings). BTW, i think that "is not a condition" for a player, belong to (let's say) a top-4 nation or league, to be named into the greatest players in their respective era. It could be happen in the 90% of cases, specially in modern times, since Euro clubs had the best players all over the world. I said, since 80s (Serie-A & Spanish league reopening their market. But, before 80s, the difference among difference leagues was closer, because main players were playing in their own countries.