The highly-rated midfielder is a top target for Jurgen Klopp's side this summer, with an opening offer of €65m (£57m) having been rejected.
However, Mateschitz has since revealed a higher bid has been tabled for Keita, though he has reiterated the club do not want to sell their prized asset.
Speaking to German publication Bild, Mateschitz said: "Lately we got a €75m offer for Naby Keita. No way! He has a contract and he will accomplish it.
“To sell him would not only be a proof of distrust to our fans but also the wrong sign for our players like Timo Werner, who is in demand too."
Leipzig sporting director Ralf Rangnick has stated in the past that even a three-figure sum would not tempt them into selling Keita.
But it is understood in Germany that Rangnick's stance is not fully supported within the club and there is pressure to make a smart business decision.
Goal also reported earlier in July that Liverpool would be prepared to increase their offer for Keita, though it remains unknown as to whether they are behind the recent €75m offer.