Marseille were one of several clubs under a settlement agreement with UEFA's Club Financial Control Body (CFCB), and needed to meet specific earnings targets.
The 'list A' is a club's main squad in a UEFA competition. They also have a 'list B' comprising younger academy players. The manager can call up players from 'list B' on a match-by-match basis.
The Ligue 1 club "failed to comply with the football earnings rule in the 2025/26 season (i.e. covering the reporting periods ending in 2023, 2024 and 2025)," UEFA said in a statement.
If Marseille fail to comply with the football earnings target in 2026/27, they will be banned from the next European competition they qualify for within the following three years, UEFA added.
Marseille were fined six million euros ($6.95 million) and received an additional penalty of four million euros for breaching the "squad cost rule", which prohibits teams from spending over 70% of their total football revenue on player and coach wages, transfers and agent fees.
AS Roma were also fined two million euros for breaching the squad cost rule.
"AC Milan, AS Monaco, Besiktas, Inter Milan, Paris Saint-Germain, Royal Antwerp and Trabzonspor met the final target of the settlement... and therefore exited the settlement regime," UEFA added.