Arsenal have signed 22-year-old Uruguayan international midfielder Lucas Torreira from Italian side Sampdoria.
The defensive midfielder featured in all five of his country's World Cup matches in Russia and becomes Unai Emery's fourth summer signing, joining Stephen Lichtsteiner, Bernd Leno and Sokratis Papastathopoulos.
Emery hailed the announcement and said: "In Lucas Torreira, we have signed a young player who is a very bright talent in the game.
"A midfielder with great quality, I have enjoyed watching his performances for Sampdoria in the past two seasons, and we all saw him do very well for Uruguay in the World Cup.
"He is a young player already with good experience, but who wants to keep on growing. We welcome Lucas to Arsenal and look forward to him joining us soon for pre-season."
The length of Torreira's contract was not disclosed by Arsenal.
With midfielders Jack Wilshere and Santi Cazorla released at the end of their contracts, Torreira's addition will be seen as key for Emery to bolster his numbers in the middle of the park.
As well as bringing in a quartet of new signings, Arsenal have extended the contracts of Calum Chambers, Ainsley Maitland-Niles and Granit Xhaka in recent weeks, while Mohamed Elneny has also agreed to fresh terms since Arsene Wenger stepped aside at the end of last season.
Arsenal are also close to completing another deal to land France Under-20 international Matteo Guendouzi.
The 19-year-old Lorient midfielder was expected to undergo his medical on Monday and his arrival could be announced later in the week.