Centre-back Koulibaly has been heavily linked with Manchester United, while Manchester City have also been credited with an interest.
Midfielder Fabian has also been tipped to move to one of Europe's elite clubs, including Real Madrid, City and Paris Saint-Germain.
De Laurentiis is not prepared to sell any of Napoli's top assets on the cheap, but he will not stand in their way if a suitable offer is made.
"If City, or United, or PSG showed up with 100million euros, I would think about it and it is probable they would leave, assuming their desire was to leave," he said.
"I don't even consider an offer of 60 [million]. If I'd wanted to win the title at any cost, today I would find myself three, four hundred million in debt."
De Laurentiis also confirmed Napoli have extended the contract of forward Dries Mertens, whose deal was close to expiring.
The 71-year-old admits he has made something of an exception to offer a player of Mertens' age renewed terms.
He said of the Belgium international, who broke Napoli's goalscoring record with his 122nd for the club against Inter in the Coppa Italia: "He's a rascal.
"We met for breakfast six months ago. It was a revelation. I met a special man, intelligent, mentally quick, a badass.
"Renewing the contract of a 33-year-old footballer is not a habit of ours, [but] with Mertens it was simple, natural.
"I'll say more: when he has stopped playing, I'd like to find him a role to continue our collaboration."
Jose Callejon's contract also runs out soon, but De Laurentiis appears uncertain whether the forward will agree to a new deal or leave on a free transfer.
"In September, or maybe October, I don't remember well, we talked to each other and clarified our intentions," he added. "I must have changed up the contract by 100,000, 200,000 euros. His manager never let us know anything. That's that. He knows the conditions."