"We need a bit of time and we will name a replacement for Vucinic in the next few days. We will call up a player we need as we have five fit strikers at the moment," Petkovic told reporters on Saturday.
Vucinic picked up the injury on Tuesday in the under-21 team's opening match against Germany at the European championship in Portugal.
Serbia and Montenegro play Uruguay in their final warm-up match later on Saturday and Petkovic said it would be a good test for his players.
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"This will be an excellent opportunity for us to get a picture of South American football. It will be a tough match because they are a skilful team," he said.
Serbia and Montenegro have been drawn in Group C with Argentina, the Netherlands and Ivory Coast. The World Cup begins on June 9.
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