[2] While visiting an uncle in Scotland in his early teens, Sau played in the youth ranks of Livingston and a local team in Gourock.

[5] In August 2010 Sau was acquired by Foggia of Lega Pro Prima Divisione by head coach Zdenek Zeman in co-ownership deals, for a peppercorn of €500,[6] scoring 20 league goals that season.

In June 2011 Foggia acquired Sau and Salvatore Burrai outright for a total of €207,000 by a closed tender mediated by Lega Serie A.

[16] In February 2023, Sau signed for Serie C Group A club Feralpisalò on a contract until the end of the season with the option for a further year.

[17] Sau made his international debut on 31 May 2013, coming on as a 49th-minute substitute against San Marino in a friendly 4–0 win at the Stadio Renato Dall'Ara in Bologna.