Canal+, which is owned by the Prisa group, believes Mediapro's announcement on Friday of an auction for La Liga TV rights was "illegal" as it included clubs who it says have signed exclusive deals with Canal+ for the next three seasons.
The broadcaster, which says it will take legal action to defend its interests, cites a Spanish court ruling that limited rights contracts to three years and which it said nullified some of Mediapro's deals.
"In that sense, and due to the lack of a framework to exploit TV rights three weeks before the beginning of La Liga, Canal+ intends to maintain and renew each season its commitment to its clients to offer the best matches," Canal+ said in a statement carried in Spanish media.
"Furthermore, it reiterates its desire to continue working to find the best framework for the 2012-13 season and underlines the need to bring the situation back to normal as soon as possible," the statement added.
The LFP, which represents the 42 professional clubs in Spain's top two divisions, said the start of the La Liga season was not under threat.
"Without any room for doubt, the league will begin on Aug. 18 as planned in the official calendar and approved and confirmed by an assembly of Spanish soccer," it said on its website (www.lfp.es).
Mediapro said on Friday it was open to offers from broadcasters for rights for first and second division matches for this season and the following season.
"Mediapro is the owner of almost all the audiovisual rights for teams competing in the first and second division for the 2012-13 and 2013-14 seasons," it said in a statement.
The 2011-12 La Liga season started a week late after the players' union (AFE) called a stoppage as part of a bid to help players whose wages had not been paid, especially those at clubs suffering from financial difficulties.