The midfielder, who has been targeted by Manchester City and Real Madrid, has praised his old boss but has reiterated that his next club will be decided within the next seven days
The 21-year-old is among Manchester City's priority transfer targets and has told Pellegrini that he will follow the Chilean from Malaga to the Etihad Stadium this summer.
Isco is currently with Spain's Under-21 squad in Israel and netted a fine solo goal in his side's 3-0 semi-final win over Norway on Saturday. Julen Lopetegui's men now face Italy in Tuesday's final.
"City or [Real] Madrid? I can't say. Pellegrini is a great coach, though, of that there is no question." Isco told reporters.
"In seven days I will decide my future.
"After the Under-21 Euros I will analyse my situation and make the best choice for my future.
"At the moment I am calm and focused on my work with the national team."