Berlin strongly protested, and a Madrid court on Sunday freed Akhanli from custody but ordered him to stay in the country.
Dogan Akhanli, 60, said his arrest Saturday at Turkey's behest was a "terrifying experience because I thought I was safe in European countries and that the long arm of arbitrariness and arrogance would not reach that far".
In a case that has further strained German-Turkish relations, Akhanli was arrested in his hotel room while holidaying in the Andalusian city of Granada, on the basis of an Interpol "red notice" from Turkey.
Berlin strongly protested, and a Madrid court on Sunday freed Akhanli from custody but ordered him to stay in the country and report weekly while Turkey has 40 days to send a formal extradition request.
"I can't imagine that as a German citizen I will be surrendered to a non-EU country, but of course I am worried," he told Der Spiegel news weekly.
He mentioned that a Swedish-Turkish journalist, named by Stockholm as Hamza Yalcin, had also been held in Spain on a Turkish arrest warrant.
Germany has dismissed the case against Akhanli as politically motivated, and Chancellor Angela Merkel warned President Recep Tayyip Erdogan's government Sunday not to "misuse" Interpol to pursue its critics.
Akhanli, speaking in a news conference televised live in Germany, described Erdogan as a president with "a despotic attitude" whose statements reflected "arrogance and paranoia".
He said that if he somehow ended up back in Turkey, this would be "a judicial and political scandal" but vowed that "they will never silence me".
Akhanli grew up in Istanbul and, in the aftermath of a military coup, was jailed from 1985-87. The biography on his website says he was tortured during his years as a "political prisoner".
He emigrated to Germany in 1991, where he was granted political asylum. In 1998 Turkey stripped him of his citizenship, and he became a German citizen in 2001.
He has angered the Turkish government by writing about the World War I-era mass killings and deportation of up to 1.5 million Armenians under the Ottoman empire.
Many historians and western nations, including Germany, label the events a "genocide" -- a term strongly rejected by Turkey.
Turkey admits large-scale massacres took place but says they were perpetrated in self-defence against what it describes as a Russian-inspired uprising by Armenians.
Akhanli was again arrested, on a 2010 return trip to Turkey, and accused of heading a terrorist organisation and having taken part in a deadly 1989 robbery.
After several months in detention, a court cleared him and he left Turkey, but the ruling was overturned in 2013.
Speaking to Der Spiegel, he charged that the accusations were made up because "Turkey wants to silence me".
Relations between NATO members Turkey and Germany, home to three million ethnic Turks, have badly deteriorated, particularly since a failed coup against Erdogan over a year ago and a subsequent mass crackdown on alleged plotters.
Erdogan has most recently angered Berlin by urging Turks in Germany to vote in September 24 elections against Merkel's conservatives and two other parties he labelled "enemies of Turkey".