WTCR will be 'worried' if manufacturer level rises further for '20

The series is entering its second season using TCR regulations, which prohibit the direct involvement of manufacturers and were designed to create an affordable customer-racing formula.

But brands may provide teams with customer support, and a number of drivers in this year's 26-car field have works deals.

Seven brands will again be on the grid this year, as Geely Group Motorsport has developed the Lynk & Co 03 for the Cyan Racing outfit responsible for Volvo's World Touring Car Championship success.

But Ribeiro said he was told by Peugeot - which was represented by DG Sport Competition in 2018 but has now pulled its support - that it was not prepared to stump up the budget required to compete with other brands, because petrol engines are still in use.

"When you see the gap in between 2018 and '19, '18 was already extremely high and competitive but this year we just go to the next step, the next level," said Ribeiro.

"Now I naturally enter into a different mode, to protect the championship from itself.

"I'm just into the mode to think what is necessary to protect WTCR from itself, just to [not] see crazy things and crazy cost inflation and direct manufacturer involvement.

"We have reached the limit - which is good, which is acceptable - to have a very strong championship [with] private teams directly supported by manufacturers, with professional drivers, technical or financial support. But not run by the factory teams directly.

"But we have reached the limit above which we should not go further. We have to keep it as it is, and not allow it to go [higher].

"If in 2020 we are higher than this, I'm worried. I would be worried."

FIA circuit championships director Frederic Bertrand agreed there was a risk the success the series has achieved could also threaten its sustainability.

Asked by Autosport whether the FIA saw any warning signs, Bertrand said: "The level of interest is growing, the level of awareness is growing, and winning becomes more important.

"The difficulty in controlling costs, or the aim we have behind that, is more to prevent the teams, which are looking on a short-term basis, to endanger the championship on a longer-term basis.

"The difficulty is always that you work on a day-to-day basis with people who are focused on their season, and as the FIA we have the same contact with the promoter.

"We are focused on a five-, 10-year plan, to see how we make it sustainable.

"So the idea is always to try to find a way to keep teams interested in being there, making business - in particular in customer racing where business is key for their sustainability.

"But on the other side we need to be careful that this does not damage or jeopardise the future of the championship."