The Blaugrana have revealed the youngster will join the Galicians for the coming season in order to gain more first-team experience in Spain's highest division.
The Brazilian had extended his contract with the Blaugrana until 2016 last month and will now be afforded the chance of significant first-team football with Luis Enrique's side, with each side confirming the deal on its official website.
"FC Barcelona and Celta have agreed to terms for the player Rafael Alcantara, who will join the Celestes for the 2013-14 season on loan," read Barca's statement. "Before the midfielder signed his new contract he showed his disposition to join another Liga team on loan in the hopes of enjoying more playing time in Spain's top flight.
"At Celta, Rafinha will join up with former teammates Fontas and Nolito.
Rafinha, 20, scored 10 goals for Barca B in 36 league matches last season. He has represented both Spain and Brazil at youth level and has been part of the Barcelona set-up since he was 13.