The midfielder is heavily linked with a switch to the Primera Division runners-up, but a deal still seems to be far away at this point
The Santiago Bernabeu side are keen to lure the 23-year-old away from his current club, but Real have no intention of letting go the midfielder for anything less than his €30 million buy-out clause.
"As of today, Illarramendi continues to be a Real Sociedad player. We are counting on him for this season," Aperribay told reporters.
"If Madrid meet his buy-out clause then it's up to them and the player to agree terms.
"I must say that Real Madrid have been behaving very well during negotiations so far."
Illarramendi, who has a contract with Real until June 2018, was part of the Spain Under-21 squad that was crowned European champions in Israel this summer.