Valencia have spoken out against proposed changes to the Supercopa de Espana format and warned Spanish football authorities not to implement the plans.

The Royal Spanish Football Federation (RFEF) has suggested changing the one-off tie between the winners of LaLiga and the Copa del Rey into a four-team tournament, which would involve the league's top two and the domestic cup finalists.

The first revamped competition has been earmarked for January 2020 and there are reports of negotiations with Saudi Arabia over hosting rights worth €150million.

LaLiga has already confirmed its opposition to the plans as the feud between Spain's top flight and its national governing body continues, and Valencia have now expressed their own deep concerns.

In a statement published on Friday, the club said: "Valencia CF have sent the Spanish Federation a burofax message warning them of the 'possible illegal nature of altering the competition in question in the present season' and advising that the club 'reserve the right to take the relevant legal action in defence of our legitimate rights and interests, should the case reach the extreme of the point being approved at the General Meeting'.

"The system for the Spanish Supercopa is established based on sporting results from the previous season, as established for the current campaign in the RFEF's Circular no. 4 communication from July 25, 2018.

"In this message, on page 31, the participating teams are clearly defined thus: 'The clubs who have won the previous season's LaLiga title and the Copa del Rey. If the same club wins both the league and the cup, the Supercopa will be between the LaLiga champions and the runners-up in the Copa del Rey'.

"Hence, the General Meeting on April 29 may only vote for this change in format for the 2019-20 season onward, as doing otherwise would result in a change akin to a variation in the relegation and promotion system, under the pretext that the LaLiga title would formally belong to a different season."