Barcelona were on the brink of agreeing a €3m sale of the 20-year-old to Girona when squad training began on 14 July, only for the deal to collapse within 24 hours after Hansi Flick intervened.
The German head coach had been impressed by what he saw from Fariñas in that first session and personally asked sporting director Deco to halt the negotiations, wanting to assess the midfielder further during pre-season, including on the club's training trip to England.
That assessment proved decisive. Fariñas so thoroughly won Flick over that his prospective exit was scrapped altogether, and on Tuesday — the final day of the Spanish transfer window — he was registered with Barcelona's first team and handed the number 4 shirt, previously worn by Ronald Araújo and, before him, by a list of club legends including Ivan Rakitić, Cesc Fàbregas, Rafa Márquez and, briefly, Pep Guardiola. He becomes the first player in 19 years to be registered with Barcelona's senior squad without having made a first-team debut, with the previous such case being Giovani dos Santos.
Flick has praised the youngster's versatility, with his favoured role as a holding midfielder complemented by an ability to play further forward or even at full-back.
"He's a committed footballer, with a lot of talent," Flick has said of him.
Competition for places in Barcelona's midfield remains intense given the presence of Rodri, Pedri, Gavi, Marc Bernal and Frenkie de Jong, meaning regular minutes are unlikely to come easily even with a squad number now secured.
Fariñas joined Barcelona's academy in 2018 after progressing through Villarreal's youth ranks, having first trained alongside future first-team colleagues such as Lamine Yamal, Héctor Fort and Tommy Marqués at cadete level.
He won the UEFA Youth League with the club's Under-19s, and last season made 33 appearances for the reserve side, Barça Atlètic, scoring five goals and providing seven assists. Barcelona's medical staff processed him alongside the rest of the first-team squad on 13 July, the same day his proposed move to Girona still looked close to completion.