In February 1973, he signed a professional contract with West Ham and on 29 August 1973, he made his debut in a draw against Ipswich Town.
However, a loss of form and injuries saw him drop out of the side,[6] and Phil Parkes' performances were good enough to keep Day out when he regained fitness.
When Eddie Gray, then manager of Leeds United, signed him in 1985, he proved to be an excellent buy and was a key figure in Billy Bremner's side in the 1987 run to the FA Cup semi-final and League play-offs.
With the re-signing of John Lukic, Day was relegated to the reserves and bench, and only made five more appearances for the first team, although he remained loyal to the club for three more seasons until he finally left Elland Road in 1993 after eight years.
On 20 July 2010, he rejoined Leeds United as chief scout to work alongside technical director Gwyn Williams.