Tomorrow we play the mixed team match with Belgium as a substitute for the Balkans, with the United States.

Belgium and the United States will face Saturday in the final of the Hopman Cup mixed teams tennis, played in the Australian city of Perth.

Belgium, who finished in second place in Group A, Serbia replaced as a finalist, winner of the group, because Serbia's Ana Ivanovic tennis player can not play Saturday because of a injury, said tournament director Paul McNamee.

"The rules are clear," said McNamee. "If the runner can not play, must be replaced by the team that finished in second place," said the head of the mixed teams tournament, involving eight nations.

Ivanovic suffered an abdominal muscle injury in the doubles to win against Belgium on Thursday with her partner and Novak Djokovic gave Serbia the turning point through to the final of the tournament, in which eight-nation participation.

United States secured the top spot in Group B after Bethanie Mattek-Sands missing the point achieved by defeating Britain's Laura Robson 6-4, 6-2. Mattek-Sands will play the final alongside his compatriot John Isner at the Belgian duo formed by Justine Henin, the former world number one, and Ruben Bemelmans.