LaLiga president Javier Tebas said Manchester City should face the "most severe sanction" available if they have breached financial regulations.
Reports on Friday said an independent panel had found City guilty on all but one of 115 charges for breaking Premier League rules.
But no official announcement has been made by the English top-flight and there is, as yet, no indication of any potential punishment.
Abu Dhabi-backed City have always strenuously denied the charges and chairman Khaldoon Al Mubarak issued a defiant statement on Saturday, underlining his conviction that City would be vindicated.
Potential sanctions could include a severe points deduction and possibly even expulsion from the Premier League, while other clubs are understood to be taking legal advice about possible compensation.
Tebas, in a lengthy social media post on Sunday, said that "equal rules for all" were essential to protect the integrity and sustainability the game.
The Spaniard, speaking at a football performance and health summit in London on Tuesday, said he had been raising concerns about City since 2017.
He said City, the dominant force in English football over the past decade, should now be severely punished.
"To have been breaking the rules for more than 10 years, however minor the breaches may have been, is very serious," he said.
"So there has to be a severe punishment for breaking the rules, not just to set an example, but because the rules were broken."
He added, "What has happened is very important, and hopefully it will be a before-and-after moment, not just in the Premier League but in European football as well, because the Manchester effect was an effect across all of Europe."
Tebas also called on the Court of Arbitration for Sport to reassess its decision to overturn a two-year European ban on City imposed by UEFA in 2020.
"In my opinion, the decisions of the CAS should be reviewed, because they lifted the sanction that UEFA had imposed on them (City)," he said.
"The sanctions were also lifted in a very questionable way. And now it has been shown that UEFA was right about the sanctions it had imposed on Manchester City."
City have been transformed under the ownership of Sheikh Mansour, whose Abu Dhabi United Group acquired the club in 2008.
They have won eight Premier League titles, a Champions League crown and multiple other trophies over the past 15 years.