The French league told Paris Saint-Germain on Thursday the club were breaking the rules by denying former France striker Peguy Luyindula the right to use first-team facilities.
Luyindula, whose contract expires at the end of the season, was not included in coach Antoine Kombouare's squad earlier this season and has been training on a pitch used by the reserves.
Under league regulations, players who have a senior professional contract with a club should share the same facilities regardless of whether they are in the squad.
"There is a pitch for the professional squad, which is guarded and which you can't access without permission, and another one, on the other side of the street, for the reserves, as well as for a local rugby club," Andre Soulier, the head of the league's legal department, told Reuters by telephone.
"According to the LFP regulations, it violates the terms of article 507 of the professional football charter.
"So until PSG ask for an exemption, we urge them to reinstate Peguy Luyindula."
Coach Kombouare has not given a reason for his decision to leave Luyindula, who won six caps for France between 2004 and 2009, out of the squad.
The club, who made a host of big-money signings in the close season after being bought by Qatari investors, said they would not give in just yet.
"Paris St Germain intend to analyse the decision dispassionately so that it can decide whether to appeal or not," PSG wrote in a statement on their website.
"Until then, the decision not being enforceable, Mr Peguy Luyindula will remain in the training group number two."comments