The Barcelona winger was due to stay in Portugal until the summer but has cut short his stay to move to Serie A, where he will aim to help revive his new club's Scudetto bid.
Cristian Tello has joined Fiorentina on loan until the end of the season after the Barcelona winger's temporary deal with Porto was rescinded.
Tello was sent to Porto for a two-year loan in July 2014 and has played 33 games in his time at Estadio do Dragao, scoring eight goals.
He has made only four starts in the league this season, however, and will now move to the Stadio Artemio Franchi to bolster a Fiorentina side challenging for the Serie A title.