Willie McStay (21 April 1894 – 1974) was a Scottish international footballer who played as a fullback.
McStay began his senior career when he joined Celtic from Larkhall Thistle in 1912, although he was immediately loaned to Ayr United, spending the following four seasons with the Somerset Park club. He had further spells away from Celtic Park during the latter years of the First World War, assisting Irish sides Distillery and Belfast Celtic, before establishing himself in the Celtic first team.
McStay earned his first selection for the Scottish national side in 1921. He made his debut in a 2-1 defeat of Wales at Pittodrie and also played in the match against Ireland two weeks later. He was not selected again until 1925 but would eventually win a total of 13 caps for his country. McStay also appeared 10 times for the Scottish League XI.
Having helped Celtic to the 1917, 1919 and 1922 League titles, In 1923, McStay played one game with New York Field Club in the American Soccer League.