Career
Tammeka
Prosa started playing football with the Tammeka Football Academy in Tartu. In August 2010, he had an unsuccessful trial at Polish Ekstraklasa club GKS BełchatóWest In the next summer he was on trial at German clubs Borussia Dortmund and VfL Osnabrück.
In 2011 Meistriliiga season, Prosa scored 22 goals in 33 games.
Flora
On 24 November 2011, Prosa signed for Flora. On 25 May 2011, he made his debut for Estonia, when he came on as a substitute in the second half of the non-Fédération internationale de football association match against Basque Country.
He made his official debut against Chile on 19 June 2011. He scored his first international goal on 6 January 2016, in a 1–1 friendly draw against Sweden.