The French Ligue 1 club reportedly sent their scouts to Gabon to watch Billiat, who was at the Africa Cup of Nations tournament with Zimbabwe.
The 26-year-old has become the talk of the town ever since his exploits in 2016 helped the Brazilians win the Caf Champions League title.
The Harare-born player is now regarded as one of the brightest prospects on the African continent.
Sundowns have, however, refused to respond to the speculation surrounding their player, but have confirmed they have not received formal offers for the attacker.
"There is nothing in writing that we have received [for Billiat]. We will only comment if there is a written offer, but at this stage, there is nothing official. We get inquiries for our players but we will only give a full statement when there is something on the table," Downs' spokesperson Thulani Thuswa told SowetanLive.
The Tswane giants are on the verge of losing Keagan Dolly to Montpellier, and it remains to be seen if they will agree to sell Billiat in the near future.