Catalonia's deposed leader Carles Puigdemont and four former advisers have turned themselves in to Belgian police on Sunday.
An investigating judge would decide by Monday morning whether to execute an EU arrest warrant issued by a Spanish judge on Friday, said Gilles Dejemeppe, spokesman of Brussels prosecutor's office.
A BBC report says, the decision may vary from arrest and imprisonment to conditional release.
Puigdemont fled to Belgium after Madrid imposed direct rule on Catalonia following an independence referendum.
Earlier, Carles Puigdemont had said he will not return to Spain unless he is guaranteed a fair trial.
The ousted Catalan president and his four associates are wanted on charges of rebellion, sedition, misuse of public funds, disobedience and breach of trust.