Colombian referee Oscar Ruiz should have explained the red card he handed to Nigeria midfielder Sani Kaita during the 2-1 defeat by Greece, coach Lars Lagerback said. Nigeria's hopes of reaching the World Cup round of 16 were dealt a huge blow after they threw away their lead to lose to Greece in Thursday's Group B clash at the Free State Stadium. They were made to pay for the dismissal of Kaita, who was shown a straight red card in the 33rd minute for inexplicably kicking out at Vassilis Torosidis when the ball was out of play. Although Kaita apologized for his childish act, Lagerback was still waiting to hear an explanation he did not get from Ruiz. "You go to the World Cup every four years and I am extremely disappointed," the Swedish coach said after the game. "The referees tell us to co-operate but you cannot speak to them after the game. "They won't tell us why the player was sent off. We cannot have this dialogue." Nigeria suffered two successive defeats against Argentina and Greece but they still have a mathematical chance to advance to the knockout phase. They have to beat South Korea, who have three points, and hope Argentina overcome Greece in the last group games. In this case, goal difference will determine who will join Argentina in the next round as Nigeria, Korea and Greece will be tied on three points. "The positive thing is that if Argentina win their game we still have a chance to qualify," Lagerback added.