It means the Spanish attacker extends his stay at the Club by a further 12 months.
Fernandez came to Blues via sister club UE Cornella in August.
He signed a short-term deal to January, which was then extended to this month.
Fernandez has had a productive season for Blues Under-23s.
He has scored seven times in 16 competitive appearances in a campaign that was disrupted by an ankle injury.
Fernandez, 19, has progressively adapted to the English game and a versatile forward he has played up front, just behind or wide for the Development Squad.
Securing Fernandez's immediate future follows on from the triggering of contract options on fellow Under-23s regulars Ryan Stirk and Jayden Reid, whilst Jack Concannon has been offered a new deal too.