Argentina needs to beat Croatia to clear its path from the three-game group stage to the knock-out round of 16.
Mercado said coach Jorge Sampaoli's squad is convinced about what's ahead, referring to the match with Group D leader Croatia.
Lionel Messi missed a second-half penalty as Iceland held mighty Argentina to a 1-1 draw in their Group D clash in Moscow.
Sampaoli is confident his troubled side will prove themselves and downplaying genius Messi's threats to quit international football.
Messi is a man on a mission as he chases his first World Cup winner's medal and will not tolerate complacency against Iceland.
Icelandic footballers are the tallest at the World Cup in Russia and Argentina is among the shortest teams playing the tournamnet.