By London correspondent Tony Hughes

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Manuel Lanzini has signed a four-year West Ham contract, according to the son of chairman David Sullivan.

The 23-year-old attacking midfielder has completed his transfer to the London club for a fee that is expected to amount to £7.5million.

Jack Sullivan Tweeted on Tuesday morning that Lanzini has agreed a four-year deal with the option to extend for a further two years.

“Lanzini is a WHU player for the next 4 seasons, with a further 2 year option,” Sullivan wrote on the social networking site.

Football Insider revealed last Wednesday that the Hammers were closing in on the permanent signing of the Argentine.

The 23-year-old attacking midfielder has been on a season-long loan at West Ham from Al Jazira in the United Arab Emirates and has impressed sufficiently for manager Slaven Bilic to sanction a permanent contract.

The Argentine is set to more than double his current salary of £30,o00-a-week.

West Ham chairman David Sullvian revealed earlier in the season that his club had a “watertight” agreement in place to make Lanzini’s loan a permanent transfer.

A deal has been in place for a number of weeks, but West Ham wanted to confirm Lanzini’s fitness after a thigh injury.

Lanzini was in sparkling form before sustaining the injury shortly after Christmas. In total, he has scored seven goals, including a brilliant goal in the 2-2 draw against Chelsea last Saturday, and supplied three assists in 24 West Ham appearances this season.