Reports emerged on Wednesday suggesting Silva's move had been held up after the Premier League club missed the deadline to register him by 14 seconds.
When contacted by Omnisport, a spokesperson for the world governing body responded: "We can confirm that FIFA has been contacted by the Football Association in connection with the registration of the player Adrien Silva and the club FC Leicester City.
"FIFA has replied accordingly providing reference to applicable regulations."
It remains unclear whether the Foxes will look to complete the reported £22 million deal if they are unable to register Silva until the next transfer window in January.
Silva has started three league games for table-topping Sporting this season, also helping the team book a place in the group stage of the Champions League with a play-off win over Steaua Bucharest.
The FA was not immediately available for comment when contacted by Omnisport.