The regional government claimed that 90% of those who voted (estimated at 43% of the population) were in favour of independence - but Spain's constitutional court later ruled the vote illegal.
The German news agency dpa reported that deputy state prosecutor Ralph Doepper, who is based in the northern town of Schleswig, said a German court would likely decide by Monday whether Mr Puigdemont would remain in custody pending the outcome of his extradition case.
"The president was going to Belgium to put himself, as always, at the disposal of Belgian justice", Joan Maria Pique, Puigdemont's spokesman said.
Issuing an global arrest warrant for Puigdemont on Friday, Judge Pablo Llarena accused the ousted Catalan leader of organising the independence referendum in October a year ago despite a ban from Madrid and "grave risk of violent incidents".
The ex-head of Catalonia is now being held at a police station.
Crowds clashed with police in downtown Barcelona on Sunday as angry Catalans protested the detention of fugitive former leader Carles Puigdemont in Germany.
Puigdemont was taken into custody as he travelled from Finland back to Belgium.
Catalonia's deposed leader Carles Puigdemont: "I will not throw in the towel".
Aside from the scenes in Barcelona, the arrest of the fugitive ex-leader of secession-minded Catalonia has sparked mixed reactions in Spain.
The Spanish Supreme Court had issued an global arrest warrant against Puigdemont past year but withdrew it in December to avoid the risk of Belgian authorities granting him asylum.
Mr Puigdemont was detained on Sunday morning in Germany on an worldwide warrant near the road leading from Denmark to Germany.
German police say Puigdemont has been detained on a European arrest warrant.
Puigdemont was removed from office at the end of October and fled to Belgium to avoid sedition and rebellion charges, while Madrid dissolved Catalonia's government.
Puigdemont's supporters, however, lamented his capture and said they hoped Germany won't honor Spain's extradition request.
His detention has seriously ratcheted up tensions in Catalonia, where separatists hold a majority in the regional parliament after elections in December.
Puigdemont's arrest came just two days after Spain's supreme court it would prosecute for "rebellion" 13 Catalan separatists, including Puigdemont and his nominated successor Jordi Turull, over their role in the region's failed breakaway bid.
He gave up his quest to reclaim the presidency earlier this month.