Marcos Ondruska is a former tennis player from South Africa, who turned professional in 1989. He represented his native country at the 1996 Summer Olympics in Atlanta, Georgia, where he defeated Goran Ivanišević in the first round before falling to Norway's Christian Ruud. The right-hander won four career titles in doubles, and reached his highest singles ATP-ranking on 10 May 1993, when he became the number 27 of the world and reached the semi-finals at the Miami Open.