Time was always going to be against Leicester, however, even after being granted a two-hour extension to the initial 11pm transfer deadline.
City are said to be confident of FIFA and the Football Association ratifying the move, while Sporting have now confirmed their intention to sell.
"Sporting Club de Portugal... informs the market that we have reached an agreement with Leicester City Football Club for the definitive transfer of the sporting and economic rights of the professional soccer player Adrien Silva," a club statement read. "The registration of the same [player] is awaiting confirmation of FIFA."
Leicester managed to get a deal for Aleksandar Dragovic successfully over the line on deadline day, meanwhile, and there were also departures for Nampalys Mendy and Danny Drinkwater late in the evening.