F1 is facing a major problem ahead of the United States Grand Prix, in the wake of the incidents on Friday involving Toyota drivers Ralf Schumacher and Ricardo Zonta.

In the first of today's two free practice sessions, most of the Michelin runner - acting on the advice of the French tyre supplier, opted not to complete full laps of the Indianapolis F1 track, and run through the pitlane rather than continue on the banked corner - where Ralf crashed - and the high speed straight that follows.

As a result only 8 drivers posted times.

The French manufacturer then issued a statement:

"Following the incidents of yesterday Michelin has controlled all the tyres that ran during the session of yesterday morning and afternoon. Despite all the checks that we have done both here and in our test facilities in Clermont-Ferrand we have not been able to understand or reproduce the problem of yesterday.

"We have explained the situation to our partners and to the FIA and we have advised on the conditions for tests, qualifying and for the race tomorrow. These decisions have been taken in the interest of the safety of the drivers.

"We have been working with our people in Clermont-Ferrand in order to identify a product that we know is also capable of running at Indianapolis."

In the second session, Michelin teams were restricted to running just ten full laps of the circuit.

Michelin now has to get permission from the FIA, ands almost certainly the three Bridgestone-shod teams, before it can introduce the new tyres, which weill be flown in from France.

These would not be available for this afternoon's qualifying session however, and it remains to be seen whether the French tyre supplier will allow its teams to run on the current tyres.

Furthermore, if the Michelin teams do 'hold out' for the tyres that are on their way from France, it would mean that they begin the race on untried tyres, which in itself raises a whole number of issues.

Therefore, should the Michelin teams miss this afternoon's qualifying session we could face the possibility of seeing a Minardi on pole.