GERARD Hutch, known as the Monk, has lost an appeal at a national court in Spain against his extradition to Ireland.
The 58-year-old's extradition is being sought by gardaí investigating the murder of David Byrne at Dublin's Regency Hotel in February 2016.
Mr Byrne (34) was shot dead during a boxing weigh-in event at the venue by a group of men dressed as gardaí.
The Director of Public Prosecutions had applied to the High Court for a European Arrest Warrant for Mr Hutch, who was arrested in Spain in August.
Spanish police apprehended the Dubliner as he sat a a restaurant table in Fuengirola on the Costa Del Sol.
The appeal heard how Mr Hutch is now a full-time resident of Spain due to threats against his life.
Judges at the Spanish court rejected his appeal against extradition, saying the decision "must stand". However, it also said: "If he is convicted, this man should be returned to Spain so he can complete his sentence here as he has residency status in Spain."
The appeal decision, made earlier this month, was revealed yesterday. The ruling states Mr Hutch, who has now lost two appeals against extradition and is being held in prison in Madrid, cannot appeal it further.
Gardaí have said they are aware of the ruling and are liaising with Spanish authorities.