Prlainović was born in Dubrovnik, Croatia and raised in Herceg Novi, Montenegro, where he came up through the PVK Jadran youth system.

He was then invited to return to Partizan but he decided to sign a contract with another Belgrade water polo club: Crvena Zvezda.

In June 2010, Fluminense triumphed in the Brazilian championship (in which a record number of foreign players (15) played that year), winning their fifth title.

On 17 September 2011, in the first round of the Adriatic League, Prlaionović scored a goal in an easy 14–6 home win against PVK Jadran.

On 26 October Prlainović scored another two goals in an easy 15–5 away win against VK Jadran Split, but this time in the sixth round of the Adriatic League.

[10] Prlainović managed to score just one goal on 3 December in a humiliating 21–0 defeat over POŠK in the twelfth round of the Adriatic League.

[14] Four days later, Prlainović scored another three goals but in the Adriatic League fourteenth-round game behind, in a 21–5 easy home win over Mornar BS.

[16] [clarification needed] Prlainović scored his first two goals at the European Championship on 17 January against Germany in a second game which the Serbs won by 13–12.