Belgium right-back Castagne has not signed a new deal and has a host of big name clubs chasing him.
Joakim Maehle has been one of Genk’s best players for several seasons and is reportedly Atalanta’s priority should Castagne leave.
Genk signed Maehle, 22, in 2017 from AaB in Denmark and he has been a shrewd investment.
During the winter transfer window, Premier League club Southampton were linked with a move for the Dane.
Two former Genk players, Castagne and Ruslan Malinovsky, are currently playing for Atalanta.
The good relations forged between Atalanta and Genk will undoubtedly be a plus if talks to sign Maehle begin.