The midfielder responded to former Real player Ruben de la Red on Twitter, who said Isco was "not performing to the required level" to be selected.
According to Joe Krishnan of the Evening Standard, Isco replied:
"Totally in agreement with De La Red, but when you don't enjoy the same opportunities as your team-mates, things change. Even so, I keep working and fighting hard as I wait for them! Hala Madrid!"
Isco has suffered a torrid time since the appointment of Santiago Solari as coach. The Spain international has been consigned to the bench despite Real lacking consistency this season.
Barcelona have expressed a passing interest in taking the player from the capital, with Blaugrana president Josep Maria Bartomeu admitting he would be willing to pursue a deal with opposite number Florentino Perez if Barca manager Ernesto Valverde wanted Isco.
Per El Partidazo de COPE (h/t beIN Sports), Bartomeu said: "If our coaches asked us for a player and they want to leave Madrid, of course we would sign them. But it has not happened since I'm here. There are no non-aggression pacts. Each one tries to make their team more competitive. Isco? For the sake of Real Madrid, I would speak with the president of Real Madrid."
Isco remains one of La Liga's greatest talents. It is difficult to fathom why Solari has denied him the opportunities a player of his ability deserves.
The 26-year-old has started only five games in La Liga this term, coming off the bench a further 10 times, but the sporadic use of the player has stopped him being able to impress the Santiago Bernabeu Stadium crowd.