The Ligue 1 side are already very active in the transfer market under new sporting director Florian Maurice.
Having qualified for the preliminary rounds of next season’s Champions League, the Brittany club know they must strengthen.
Rennes face stiff competition for both, so are also looking to Belgium and 21-year-old Jhon Lucumi.
A left-footed central defender, Lucumi has won three caps for Colombia and is very highly-rated.
He featured against the likes of Liverpool, Napoli and RB Salzburg in this year’s Champions League, scoring against the Austrians.
According to Het Nieuwsblad, Rennes have made an offer of more than €10m for Lucumi.
However, they will have to try again with Genk rejecting their opening bid.
The Belgian club are ambitious and want to keep their top players, so will only accept irresistible offers.
Rennes must now decide whether to submit a second offer for Lucumi, who is under contract with Genk until 2022.