Ahead of the return to Championship action, the Spanish forward becomes another option for Pep Clotet.
Blues recently took up the year's option on Fernandez's contract.
That came off the back of a fine campaign for the Under-23s.
Fernandez scored seven times in 16 competitive appearances.
Jayden Reid (number 49) and Nico Gordon (50) were given squad numbers in the weeks before the season was suspended, as well as Kyle Hurst (51).
Fernandez, Reid, Gordon, Hurst and Ryan Burke have been training with the senior squad continually since Blues returned to Wast Hills last month.
Burke - who was an unused substitute at the Leicester City FA Cup tie and at Portsmouth in the Carabao Cup - has squad number 45.