The ousted Catalan president, Carles Puigdemont, will find out next week whether he will be sent back to Spain to face rebellion charges.
The decision on whether to extradite him for trial in Madrid will be made by a judge in Brussels on 14 December.
Mr Puigdemont fled to the Belgian capital after Catalonia’s parliament declared independence on 27 October, saying he would not get a fair trial back home.
He has launched his campaign for the new Catalan parliamentary elections, to be held on 21 December.
As Mr Puigdemont awaits the decision from a Belgian judge, a Spanish judge decided that the sacked vice president Oriol Junqueras and three other separatist leaders will remain in prison during a probe over their role in Catalonia’s independence drive.
Judge Pablo Llarena said Mr Junqueras would likely repeat his alleged offences of rebellion, sedition and misuse of public funds if he was released.
Judge Llarena’s decision sparked outrage among independence supporters, with Catalan parliament speaker Carme Forcadell – who is also under investigation over her role in the campaign – tweeting: “We want you back home. We will turn sadness into energy and we won’t stop until you are free.”
But six other former ministers who were also remanded in custody last month will be released on bail of £82,000.
Campaigning for the Catalan elections officially begins at midnight, with Madrid having called the polls after sacking Catalonia’s government and suspending the region’s autonomy.
Pro-independence parties won 47.8% of the vote in 2015 but this time they are polling at around 45% and their support could be split, with Mr Puigdemont and Mr Junqueras running on separate tickets.
The former president launched his campaign last month from Brussels with a flurry of high-profile media appearances and a demand that he be returned as the “legitimate” president of Catalonia.
Mr Junqueras leads the ERC party, which is ahead in the polls.
Spanish Prime Minister Mariano Rajoy and fellow opponents of Catalan independence are hitching their hopes on a record turnout to ensure support for unity with Spain.