Sporting Lisbon have claimed that they were forced to sell defender Eric Dier to Tottenham Hotspur due to an agreement already put in place between the player and the club's previous owners.

Spurs announced on Thursday that they had agreed a five-year deal with Dier, but Sporting have indicated that they were unable to offer the defender a fresh contract in an attempt to keep him in Portugal.

An official statement read: "Sporting Clube de Portugal announces that during July, the club started negotiations with Eric Dier over the renewal of his contract.

"Unexpectedly, Sporting were confronted by the father and the official representative of the player with a transfer offer from Tottenham Hotspur, who referred to the current administration an agreement signed by previous directors and administrators, which obliged a sale of the player for a sum not exceeding €5m (£4m), or for Sporting to equal the proposed salary, which is impossible due to the wage structure in place, the ongoing financial restructuring and necessary sustainability of the club.

"Additionally, Sporting were informed that the player does not want to stay at the club even if the proposed salary was matched. And even if Sporting received a superior offer, whether in terms of a transfer bid or salary, from another club, the player would not accept it.

"Given the constraints outlined above, Sporting announces the sale of all economic rights for the player Eric Dier to Tottenham Hotspur, for the value of €5m net, without any future rights or guarantees."

Dier, who has won five caps for England's Under-21 side, leaves Sporting having made 26 appearances for the first team.