The transfer was announced by the Spanish side on their official website, and Ajax coach Frank de Boer believes that the 22-year-old is a "quality" player.
Ahead of the move, the 43-year-old had told Voetbal International: "He's a quality player who knows what it's like to perform at the highest level.
"Bojan is a roving attacker like a Viktor Fischer-type. He's not a real right-winger like Isaac Cuenca, but I would like to have him."
The Spanish international has spent the past two seasons on loan at Roma and AC Milan.