Kacar heralds from a sporting dynasty and his appearance at the Beijing Olympics in 2008 saw him follow in the footsteps of uncles Slobodan and Tadija - both boxers who won medals at the Moscow and Montreal games.
Kacar has long been heralded as a real prospect after making his debut for FK Vojvodina aged just 16.
He soon emerged as a first-team regular and in 2007, the same year he made his debut for Serbia Under-21s, he was called into the senior squad.
Kacar once scored five goals in one game for Serbia's Under-21s in a qualifying match for the 2009 European Under-21 Football Championship.
He made his debut for the senior Serbia side against Kazakhstan in 2007 and has gone on to win 15 caps for his country
In 2008 German side Hertha Berlin paid £3million for him and in his debut season Kacar showed his potential with seven goals, predominately from midfield, although he is adept in defence and can also play as a striker.
The 23-year-old has impressed at Hertha and a number of clubs across Europe, including Manchester United, have been credited with an interest.
With Hertha suffering relegation this season Kacar could use the World Cup as the perfect opportunity to put himself in the shop window.