The defensive midfielder featured in all five of his country's World Cup matches in Russian Federation and becomes Unai Emery's fourth summer signing, joining Stephen Lichtsteiner, Bernd Leno and Sokratis Papastathopoulos.
Arsenal unveiled their new man in a Uruguay-themed video on their social media accounts.
Arsenal are embroiled in a battle with Everton and West Ham United to sign Sevilla midfielder Steven N'Zonzi in the summer transfer window, according to a report in France.
The new signing has a tattoo featuring a lion on his arm and said the king of the jungle best represents him and his people: "It's true that a lion represents strength and the spirit we Uruguayans have inside".
UC Sampdoria announces that it has relinquished the rights to the sports performances of the player Lucas Sebastián Torreira to Arsenal FC.
Manager Unai Emery told the club's official website: "In Lucas Torreira, we have signed a young player who is a very bright talent in the game".
During his two years at Sampdoria after joining from Pescara, Torreira made 74 appearances and scored four goals for the club.
Tenfield says Torreira will earn £50,000 a week at Arsenal with his move potentially being confirmed today.
The 22 year-old has just returned from representing his country at the World Cup in Russian Federation, where he played in all five matches as they progressed to the quarter-finals.
"We welcome Lucas to Arsenal and look forward to him joining us soon for pre-season". Ozil was handed his favoured No 10 shirt after the departure of Jack Wilshere.
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