In his prime he was often considered one of the best and most complete left-backs in the world in his era, rivaled only by Giacinto Facchetti, Nílton Santos and Silvio Marzolini.

Schnellinger left Milan in 1974, and retired after a season back in his native Germany with Tennis Borussia Berlin.

[6] His only international goal came in stoppage time to draw 1–1 in the thrilling semi-final of the 1970 World Cup against Italy, which later became known as the "Game of the Century".

His goal led to the famous German TV commentary line by Ernst Huberty "Ausgerechnet Schnellinger!"

[9] Schnellinger later lived in Milan's suburb of Segrate where he worked as a businessman after retirement from football.