It was in his home town of Los Palacios y Villafranca, in the province of Andalusia, that the young Fabian discovered football. His appetite for foot ball led him to the Real Betis youth academy at the age of eight, where he honed his skills as a midfielder at all youth levels.

In 2014, having just turned 18, he joined the Spanish club's reserves, with whom he would be crowned Spanish D2 champion. He made his debut for the first team the following summer, before going on loan to Elche CF duri ng the winter to practise his skills. Napoli's scouts then made a move for the tall (1.89m) creative midfielder to join the Serie A side. Under Ancelotti and then Gattuso, Ruiz became an automatic starter, which sent him strai ght to the Spanish national team (15 caps).

With the Azzurri, the regista eventually made no less than 166 appearan ces, including 32 at European level (22 goals, 15 assists), before deciding to cross the Alps for a new challenge. It was in the summer of 2022 that the 26-year-old Andalusian moved to Paris Saint-Germain for the big move.