The Brazilian fullback joins the Asturian club for the 2016/17 season.
The highly rated La Masia graduate will play this season under the guidance of Paco Jémez.
Currently at Villarreal, the midfielder also wishes for a return in what could be his first full season in Blaugrana.
The Celta winger is Luis Enrique's main target this January and the club is still trying to make it happen.
The midfielder returns to Upton Park for another season.
The attacking midfielder has more competition, but Emery's tactics give him a unique chance.