Arsenal announced on Tuesday they had signed Porto midfielder Fabio Vieira on a long-term contract for a reported fee of £34 million ($42 million), including add-ons.
The 22-year-old came through the Portuguese club's youth system and made 27 appearances during last season's Primeira Liga triumph.
Arsenal manager Mikel Arteta said: "I am very excited that we have identified and signed such a special talent. "Fabio is a very creative player that will bring high quality and versatility to our attacking play." Arsenal have already bought Sao Paulo teenager Marquinos to bolster their squad but Vieira is expected to slot straight into the first team.
The Gunners have also signed USA goalkeeper Matt Turner. The skilful playmaker made 39 appearances for Porto last season, scoring seven goals and contributing 14 assists. "Fabio is a player with special qualities who is comfortable with the ball in the final third of the pitch," said Arsenal technical director Edu.