Toro Rosso boss Franz Tost fears that Formula 1 is running out of time to reach crucial decisions about the sport's future.
A planned overhaul of the sport for 2021 will introduce new sporting and technical regulations, including a major revamp in engine rules.
But there is still a lack of final agreement between teams, the FIA and the commercial rights holders FOM, leading to suggestions that changes to power units might have to be put back.
“Once more the FIA and FOM has to come up now with solutions, because time is running away,” Tost said in Suzuka at the weekend.
“We are talking about 2021 and we still don’t have a 100 per cent fixed regulation for the chassis and for the power unit," he continued. "This needs to be clarified as soon as possible."
Tost said that the big problem with the current regulations was that three teams were so far ahead of the rest, creating a split championship.
"There are three teams and the rest are far behind," he complained. "The FIA and FOM must come up with a regulation from the sporting side and the technical side.
"Formula 1 is entertainment and currently," he pointed out. "Fortunately thanks to [Lewis] Hamilton and [Sebastian] Vettel, we have two drivers who keep this entertainment on a higher level.
"But a minimum of five or six drivers [must be] able to fight for the championship, because this is what the spectators want to see."
Tost's view was backed by Sauber team principal Frederic Vasseur.
“[We need] a solution to allow talented drivers in a small team to be not too far away from the podium," Vasseur said. "Today we are far away from this. We are not racing in the same competition."
Like many other team principals, Tost was also concerned about the cost impact of any forthcoming changes to the rules.
"They must also look that the costs come down," he said. “The cost cap is I think an idea that can be realised."
But he didn't want to see innovation and development adversely impacted by the rules.
"There is always enough space and room for the manufacturers to develop, for example, the power unit or whatever, and that Formula 1 stays at the pinnacle of motorsports."
Despite Tost's concerns, FIA president Jean Todt has recently indicated that the sport is “very close” to reaching a final agreement on 2021 regulations.
However he admitted that the sport was unlikely to attract new manufacturers into the sport alongside Mercedes, Ferrari, Renault and Honda by changing the engine regulations.
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