The 20-year-old midfielder has been in impressive form for the Spanish outfit this season and has been linked with several European clubs, including Manchester City.
"It is hard to say what a young player like him can achieve, but he really has all the qualities to become a star," Sanz told Goal.com. "He will become an important part in the history of the national team and Spanish football.
"He is a player who only needs time and experience at the highest level. He already proved his worth in his first year at Malaga, and has made another step up this term. He is Malaga's star man.
"He is rated very highly in European football, not just in Spain, but also in England for example. His performances in Europe in the Champions League have not gone unnoticed elsewhere. Additionally, his debut with the national team has only further increased his reputation."
Isco joined Malaga from Valencia in the summer of 2011.