"Bale stands out in a solid Welsh team as the one player who can turn the game around by himself," Kostic, who plays for Bundesliga side Hamburg SV, told Serbia's Sport Klub television channel on Tuesday.
"But we have our own match winner in Dusan Tadic," he said. "We've made a good start in the qualifiers and are confident that we can get a result in Cardiff."
The Serbians top Group D with seven points from three games, ahead of Ireland on goal difference. Third-place Wales have five points and Austria have four in what is shaping up to be a fiercely competitive section.
Tadic has carried Serbia's effort by scoring three goals and setting up the other five, with Kostic providing adequate support on the opposite left flank.
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"Dusan and I work well together and I hope we have another productive evening against Wales," said Kostic.
"It doesn't matter who scores, I will always do what's best for the team."
Serbia are aiming to reach their first major tournament since the 2010 World Cup in South Africa.
(Writing by Zoran Milosavljevic)
