The three-way Formula One title fight between Michael Schumacher, Juan Pablo Montoya and Kimi Raikkonen may be tilted in Schumacher's favour by a new tyre ruling.
Montoya's tyres have helped him to second in the championship
The sport's governing body, the FIA, has ruled that, in some circumstances, the Michelin tyres which have recently helped Montoya and Raikkonen drive faster than Schumacher could be illegal.
The ruling is understood to have been prompted by a complaint from Ferrari and their tyre supplier Bridgestone, although both have denied it.
F1 regulations state that the part of the tyre that grips the track - the tread - can be no more than 270mm wide.
The Michelin tyres conform to that standard before a race but the FIA believes that during a race a bigger area may be gripping the road, giving them an advantage over Bridgestone.
"We feel there may be systematic use of a part of the tyre as tread that doesn't look like tread when the tyre is submitted for scrutineering," said an FIA source.
The ruling may mean that Michelin has to scrap its current tyres and has reportedly led to suggestions from Michelin's boss Pierre Dupasquier that the teams who use his tyres might boycott the next Grand Prix, in Italy on 14 September.
"It is possible that the five teams using Michelin tyres will not turn up in Monza," he told The Daily Telegraph newspaper.
"Our partners would have to spend a lot of money without any guarantee that they would not be disqualified. It is up to them to decide."
Renault technical director Mike Gascoyne said the ruling opened up all sorts of problems with regard to interpretation and would likely lead to massive confusion.
"What they're saying is the way the Michelin tyre deforms and then the part of the rubber that comes into contact with the road when they look at it after the race could be wider than 270mm," Gascoyne told BBC Radio Five Live.
"The trouble is the contact patch of the tyre is changing constantly when it's cornering - the contact patch is moving around the tyre. When the tyre hits a kerb, it could be right on the side or edge of the tyre.
"So how do you decide whether it was bigger than 270mm at any point, or whether it was random, touching a corner, or a kerb on a corner, or whether it was happening all the time and giving an advantage?
"How do you decide that? I don't know. I don't even know what my tyres have been like after a race, whether we conform or not."
World champion Michael Schumacher currently leads the drivers' standings by one point from Montoya and two points from Raikkonen.
In his last race, Schumacher finished eighth and was lapped by winner Fernando Alonso, who was using Michelins, as were the other six drivers ahead of the reigning champion.