Siegmund Walter "Sigi" Nissel OBE (3 January 1922 – 21 May 2008) was an Austrian-born British violinist who played second violin in the Amadeus Quartet and served as its administrator.

During World War II, Nissel was interned as a "friendly enemy alien" in Onchan Camp on the Isle of Man where he met the violist Peter Schidlof and later the violinist Norbert Brainin.

The Amadeus Quartet, informally known as the Wolf Gang, gave its first concert in London in 1948.

He married the statistician Muriel Griffiths in 1957, and they had a daughter Claire and a son Daniel.

Nissel became a teacher of young quartets at the Royal Academy of Music, and died in London.