In 1905, City was found guilty of malpractice relating to payments of its players, and the entire squad was suspended from playing football.

When the ban was lifted on 31 December 1906, Turnbull moved to City's crosstown rivals Manchester United, along with Billy Meredith, Herbert Burgess and Jimmy Bannister.

Along with Meredith, he helped the club to their first championship in 1908 and the 1909 FA Cup, scoring the only goal in the final, against Bristol City.

[1] Turnbull received a lifelong ban from football in 1915 along with several others players after being found guilty of match-fixing.

Two of Turnbull's sons, Alexander Jr. and Ronald, signed amateur forms with Manchester United in August 1932, but neither managed to follow in their father's footsteps and they were released before making an appearance for the club.