Gomis, 25, who helped Senegal reach the final of the recent Africa Cup of Nations in July, moves to France for a fee of around one million euros ($1.1m), according to the sources.
Gomis played an important role for Senegal at the Cup of Nations in Egypt as he stepped up to replace Edouard Mendy after the first-choice goalkeeper broke a finger in his left hand during the group stage.
Senegal ultimately lost the final against Algeria but Gomis was voted man of the match in the semi-final against Tunisia, in which he saved a penalty.