In a tactical sense, the interesting thing about international football is the fact managers are presented with a fixed pool of players.
If there’s a weakness, they have to play someone out of position or solve the problem through a clever tactical plan—they can't just go out and sign someone else.
This means a side's key player isn't always their best player. Often, the key player is someone playing a distinctive role, someone forced to adapt to a position he is not familiar with, or someone who provides a unique quality compared to the rest of the squad.
Here, then, is the key player for each of the 32 competing nations at this summer's World Cup.