Sakho and Lanzini celebrate
Lanzini (right) scored at Stamford Bridge at the weekendGetty Images

West Ham United have signed Manuel Lanzini on a four-year deal for a fee of around £9.4m ($13.4m). The 23-year-old attacking midfielder has impressed since joining the Hammers on loan and has now finalised the details of his switch from UAE outfit Al Jazira.

The Argentine was hugely influential in West Ham's 2-2 draw against Chelsea at Stamford Bridge at the weekend, scoring his team's first goal, and the club have moved to secure his services on a long-term basis. West Ham will officially complete the deal when the transfer window reopens this summer.

"You can hardly get a player for [12m euros]," West Ham's co-chairman, David Sullivan, told the Daily Mail. "We've just signed Lanzini on a permanent deal for that sort of money."

Meanwhile, Jack Sullivan, David's son, also confirmed Lanzini is to sign a four-year deal with West Ham, having excelled since moving to the Premier League from the UAE. "@jsullivanwhu: Lanzini is a WHU player for the next 4 seasons, with a further 2 year option," he tweeted.

Speaking after his outstanding performance against Chelsea at the weekend, West Ham boss Slaven Bilic admitted to being surprised by the quality of Lanzini's performances. "When I signed him I would be lying if I said that I was thinking he would play at such a consistently high level," he said, as quoted by the Daily Mail.

"I had no idea that by this time of the season, he would have played so well. It's special enough wearing the No 10 shirt for River Plate, at only 18 years of age, it is after all a very famous number, but Lanzini has developed with us and produced some brilliant football.

"Perhaps I didn't quite realise how good he can be. At 23, he is willing to take responsibility, and copes easily with the pressure."