While not releasing the fee involved - believed to be €35m - ASSE admits it is a record for the club.
In a statement, the club declared: "AS Saint-Étienne reached an agreement on Tuesday evening with Leicester, the current leader of the English Premier League, for the transfer of their defender Wesley Fofana.
"The amount of this transfer is the largest ever obtained by the club.
"The decision to sell the player was taken collegially by the Management Board and the shareholders. ASSE accepted Leicester's exceptional offer, especially given the uncertain economic context caused by the health crisis."