Garzon had been expected to give a preliminary statement to judicial police as early as Thursday, but that process was delayed, reportedly due to health reasons. Earlier Saturday, the justice department said Garzon's first appearance before a judge had been postponed until Sunday.
A blood-soaked Garzon was photographed after the Wednesday crash being escorted away from the wreckage, at first by civilians who had hurried to the scene of the accident and then by police, but it is not clear just what his medical status is.
Unconfirmed media reports said that Garzon had injured ribs.
The train's eight passenger carriages packed with 218 passengers blazed far over the speed limit into a curve and violently tipped over. Diesel fuel sent flames coursing through some cabins.
Investigators are examining recording devices from the train but have not officially said how fast it was going when it derailed.
An American passenger, Stephen Ward, said he was watching the train's speed on a display screen in the carriage — and it indicated it was going 194 kph (121 mph), more than double the 80-kph speed limit.
The president of Adif, the Spanish rail agency, said that the driver should have started slowing the train 4 kilometers (2.5 miles) before the dangerous bend. He said signs clearly marked this point when the driver must begin to slow.
Normally, police take a first statement that is then examined by an investigating judge who must then take testimony within 72 hours of the arrest. That deadline is 7:40 p.m. Sunday.
Although that initial court hearing would be closed, it would give hints about the status of the investigation. The judge would decide whether to jail the driver as an official suspect, release him on bail, or release him without charges. If a judge finds sufficient evidence for a criminal trial, the suspect will be charged and a trial date set.