Talking to Sky Sports, Whitbread's agent Kevin Moran spoke of Genk's interest in the the defender as they look to strengthen their squad for next season.
"It is true that Genk have made an enquiry for Zak," revealed Moran. "They are in Europe next season and they have expressed an interest in him.
"They have made an enquiry to Millwall, but that is as far as it goes at the minute."