English powerhouse City were charged in February 2023 with over 100 alleged breaches of the league's financial rules, with the club vigorously denying all charges against them.
Yet more than three years later no verdicts have been made public, with an independent commission having heard the case between September and December 2024.
Tebas said his problem was not so much the length of time being taken to make a ruling, but rather the drawn-out process had created "uncertainty" regarding the application of rules, with other clubs charged and sanctioned over rule breaches all within the same period.
"I understand that it's a failure (of governance) - this happened with Manchester City and other clubs are looking and watching and listening," Tebas said Thursday during at a media briefing at the Financial Times Business of Football Summit in London.
"(Other clubs are) being fined, having points deducted, and that's fine if you don't abide by the rules. But Manchester City has impunity. I speak to a lot of Premier League clubs, and the majority don't understand this either. That makes the institution weaker."
The chief of Spanish football's top flight added: "It's not just the delay, it's the general situation. When a great institution like the Premier League, when you have to have rules for financial fair play, you need to have a lot of legal certainty in the competition and among clubs."
City have previously said they have a "comprehensive body of irrefutable evidence" to prove they've done nothing wrong.
Premier League chief executive Richard Masters was asked about the City case when he appeared at the same event later on Thursday.
"I can't talk about it, I can't talk about the timing of it," he said.
Asked whether the case had made the Premier League consider if there might be ways to have a quicker process should a similar incident arise in the future, Masters replied: "I simply can't comment. Having spent three years not commenting, I'm not going to start now.
"Stepping aside from that (specific case), any regulator wants its judicial system to be efficient and work swiftly. That's about as far as I can go."