The once unfathomable prospect of a World Cup without Lionel Messi and Argentina could become reality on Tuesday as South America's thrilling 2018 qualification battle reaches its climax.

Two years after Argentina kicked off their troubled campaign with a 2-0 defeat at home to Ecuador, Jorge Sampaoli's side travel to Quito to face La Tri once more with their hopes hanging precariously.

The two-time World Cup-winners head into the final round of games in sixth place overall, outside the top four positions which grant automatic qualification and trailing fifth-placed Peru, who occupy the playoff spot, on goal difference.

Yet with only two points separating third-placed Chile (26 points) with seventh-placed Paraguay (24), any number of permutations are possible.

Argentina can simplify the equation for their fans, however, if they manage to take all three points.

A victory would guarantee they finish no worse than fifth place, putting them into a two-legged play-off against New Zealand they would be expected to win.