Twenty-year-old Day played youth football for Crystal Palace, where he signed a two-year scholarship in 2014.
He left Selhurst Park after one year of his scholarship and joined Barnet as a second-year scholar for the 2015/16 season.
He made his League debut when he came on as a substitute against Crawley Town on the final day of the 2015/16 season.
Day joined Bostik League Premier side Staines Town on loan for a month in September 2016 and this loan was later extended beyond January 2017, and he totalled twenty-eight appearances for the Swans.