Koulibaly has been linked with a move to Manchester City, while Roma are reportedly the frontrunners to sign Milik.
Speaking on Wednesday, De Laurentiis said the duo would depart Napoli for the right price.
“Koulibaly and Milik are both leaving, market permitting,” he told Canale 21.
“So, if the market allows these two talented players to leave, we will know how to replace them.
“Otherwise, we will talk about them next year.”
Koulibaly, 29, has developed into one of Europe’s leading centre-backs since arriving at Napoli from Genk in 2014.
The Senegal international is contracted until 2023, but has been linked with a £57.7million (€65m) move to City.
Milik, meanwhile, has spent four seasons at Napoli and netted 14 goals in 35 games in all competitions in 2019-20.
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