But the Malaga chief also confirmed Isco has a €21m buyout clause in his contract, and the La Liga club would be left powerless to stop him leaving if an interested party activated the clause.
Isco is a product of the Valencia youth academy but moved to Malaga in 2011, and the 20-year-old has represented Spain at every youth level from under-16 through to under-23.
And the Spain star has attracted the interest of a number of Premier League clubs, including Manchester City and Liverpool.
But his employers in Spain are very keen to hold onto the playmaker.
"Isco? He is our player, so important for the club, he is not for sale," said Husillos on Italian source calciomercato.com.
"But you all know that there is a buyout clause. If a club will pay it, it would not depend anymore on us."
And when asked if Isco could leave the club for €21m, Husillos said: "Exactly, but we would like to hold him here with us."
The attacking midfielder first emerged as a target for Liverpool in the summer, as Brendan Rodgers looked to add creativity to the Reds midfield. Liverpool are still thought to be keen on the Malaga ace, and could reignite their interest when the window opens in January.
But Manchester City are thought to have entered the race to sign the youngster, after Isco put together a string of fine performances in the Champions League and La Liga in the early part of this season. Roberto Mancini could look to strengthen his squad in January, after a relatively subdued summer window - at least compared to previous expenditures.