The club said the 26-year-old had signed a four-year contract in a deal reported by the Greek media to have involved a transfer fee of between 1.5 and 2.3 million euros.
The defender played 14 times for the Spanish national team. He had been with Real Madrid since 1997 but struggled to break into the first team, leading him to spend a spell on loan at Leeds in 2003 under then boss Terry Venables.