The Foxes’ appeal to FIFA to secure the registration of Portuguese midfielder Silva was on Wednesday morning rejected by world football’s governing body.
Leicester and the Football Association had asked FIFA to ratify the transfer after the paperwork for Silva’s £22million deadline day move from Sporting Lisbon was submitted 14 seconds late.
That request was denied and, as things stand, Silva will now not be registered to play for Leicester until January.
A Leicester spokesman said: “We cannot hide our disappointment or that of the player at the short-term consequences of the decision.
“We maintain, and have made strong representations to FIFA’s Players’ Status Committee, that all parties involved in Adrien’s transfer fulfilled their obligations, consistent with FIFA regulations and within the required timeframe.
“The club is reserving its position in relation to whether it will decide to appeal the decision to the Court of Arbitration for Sport.
“The club and its staff will continue to work with Adrien to hopefully minimise the impact that missing a substantial period of the season may have on the player, while continuing to prepare the squad for the games ahead.”
FIFA withheld the International Transfer Certificate because the data input into its Transfer Matching System was received by the FA moments after the deadline.
Silva is currently in limbo, unable to train with Leicester and having been left out of Portugal’s squad for their final World Cup qualifiers against Andorra and Switzerland this month.
Earlier on Wednesday, a FIFA spokesman said: “We can confirm the following decision of the Single Judge of the Players’ Status Committee: the petition made by The Football Association for permission to request the International Transfer Certificate for the player Adrien Silva and subsequently register the player for its affiliated club, Leicester City FC, is rejected.”