And they state that Mane is trying to persuade his Senegal team-mate to join him at Anfield.
Mane publicly urged the Merseyside outfit to bring in Koulibaly in July, as he lauded him as one of the world's best defenders.
He said: "Kalidou Koulibaly is an excellent defender, and one of the world's best in his position.
"I would be very happy to play alongside him at club level, as I have known him for years."
Before adding: "We first got to know one another at Metz before meeting up once more in the Senegal national team.
"No club could refuse the chance to have Koulibaly in their squad.
"In any event, it would be a pleasure for me to play for Liverpool together with him. He would be more than welcome here."