Adam Scott Mathieson Duncan[1] (2 November 1888 – 3 October 1976) was a Scottish football player and manager, who played as an outside right.

He made over 100 appearances for Rangers, played in England for Newcastle United, winning the Football League title in 1908–09.

He left in October 1925 to take over as secretary-manager of Cowdenbeath and had seven successful years at the club, keeping them in the Scottish First Division throughout his time in charge.

Duncan remained with Ipswich Town as manager for 18 years, winning the Third Division (South) title in the 1953–54 season.

He was honoured with a testimonial match at the end of the 1957–58 season against Norwich City at Portman Road, which Ipswich won 3–1.