The 40-year-old Romero, from Andalusia, attracted criticism when he allowed Real Madrid boss Mourinho to remain in the technical area during the 2-0 Liga win over Rayo Vallecano on February 17.
Mourinho had left his technical area to protest the decision not to show Rayo’s Lass a second yellow card after he was penalised for deliberate handball – Real defender Sergio Ramos had been dismissed for exactly the same offence earlier in the match.
The incident resulted in a fall-out with referee chief Manuel Diaz-Vega, and while there is no suggestion he was asked to step aside, it is believed Romero felt he could no longer continue in his role.
Ironically Romero is the only Liga referee to have dismissed Mourinho twice in his career, but his decision not to do so a third time appears to have ended his career.
The Antequera-born official made his Liga debut in 2007, and had refereed 87 top-flight matches. The LFP must now find a referee for the weekend match between Espanyol and Real Valladolid, which Romero had been set to oversee.