Eric Dier
Dier's father and agent brought forward Tottenham's offer during talks over a new deal.Getty

Sporting Lisbon have hit out at Eric Dier's father and agent for their role in the defender's move to Tottenham Hotspur.

Cheltenham-born Dier is a product of Sporting's youth system, but is poised to return to these shores, pending a medical, after the north London club matched the 20 year-old's £4m release clause.

The England Under-21 international will become the third signing of Mauricio Pochettino's reign at White Hart Lane, but the circumstances behind the move have enraged his former club.

After a season where Dier had begun to impose himself on the first team at the Estadio Jose Alvalade, the Portuguese club was eager to tie the youngster down to a new deal. But during those talks the defender's representatives brought forward Tottenham's bid, which matched a release clause put in place by Sporting's previous administration, and a contract offer that turned the youngster's head and paved his way to north London.

"Sporting Clube de Portugal announces that during [July] the club started negotiations with Eric Dier over the renewal of his contract," read a statement on Sporting's official website.

"Unexpectedly, Sporting, SAD was confronted by the player's father and official representative with a bid from Tottenham Hotspur, with that bid activating a clause agreed by previous boards of directors for the sale of the player for an amount of €5m [£3.9m, $6.7m] or more, unless the personal terms offered as part of the bid are matched.

"Due to the club's current salary policy, the respective balance within the squad, and the ongoing financial restructuring underway at the club, it was not possible to match the proposed terms.

"Furthermore, Sporting, SAD was also informed that the player did not want to remain with the club even on equal terms, and that any equal or improved personal terms would not have been accepted.

"In light of the above Sporting, SAD announces the complete sale of the economic rights of the player Eric Dier to Tottenham Hotspur for €5m, without any future rights relative to the player.

"Despite the above mentioned events, Sporting, SAD wishes Eric Dier all the best in his career."

Dier moved to the Portugal's capital as a 10 year-old and progressed through the club's famed youth academy, signing his first professional contract three years ago.

He is the third player to join Spurs this summer, following the arrivals of Ben Davies and Michel Vorm from Swansea City.