Pre-contracts
A club may sign a pre-contract with a player while he is still with another club, by which the player agrees to move to the club at a future date, for example, after his contract with his current club expires.
Another situation may be where the current club is also a party to the pre-contract, and the transfer is conditional, for example, on a fee being agreed between the clubs or terms being agreed between the player and the new club, or the transfer is intended to take effect only after the player reaches a certain age.
The pre-contract is intended to prevent a third club from signing the player while details are still being negotiated or when the future date arrives.
As the player's registration remains with the current club, however, the existence of a pre-contract may be unknown to other clubs who wish to sign the player.
Read more about this topic: Transfer (association Football)