William John McStay (born 26 November 1961) is a Scottish former footballer and manager of clubs including Sligo Rovers, Újpest FC, Ross County and Celtic Nation.

McStay made his debut on 2 April 1983 when he came on as a sub in Celtic's 3–1 home win over Motherwell and went on to make 65 league appearances, including 10 as a substitute, scoring two goals.

[16] McStay led his side to their first trophy as Celtic Nation on 29 April 2014, defeating Aspatria 3–0 in the Cumberland Cup Final.

[20] Matters reached a head in July 2014 when owner Frank Lynch sold the club on to former chairman Steve Skinner.

[12] Their younger brother Ray had a less notable career as a footballer after also starting out at Celtic, and their father John worked as a scout for the club.