The Ligue 1 club is expected to appeal the ruling by FIFA's Dispute Resolution Chamber following a complaint by Premier League Watford. Marseille also received a fine of "a little over two million euros", according to the source.
The 22-year-old Gueye, who is with the Senegal squad at the Africa Cup of Nations in Cameroon, has been suspended from all competitions for four months. After starting his career at Le Havre, Gueye was due to become a free agent in the summer of 2020. In April of that year, he signed a pre-contract with Watford then agreeing a deal with Marseille.
Gueye played for France at under-18 and under-19 level before opting to represent Senegal, where his parents are from, last October. He came off the bench for Senegal in their opening game but did not figure in Friday's 0-0 draw with Guinea after his team learned of the ban.