Sebastian Vettel fears that the power advantage of the KERS cars could make it difficult to fight for victory in Sunday's Italian Grand Prix despite expecting his Red Bull to be competitive at Monza.
McLaren, Ferrari and Renault are all running with the energy recovery system, which offers an 80hp power boost for six to seven seconds per lap, and Vettel believes that the true performance benefit of the system will be revealed in free practice tomorrow.
"We should be in good shape, but it depends how big the effect of KERS is - especially with Renault running it," said Vettel.
"How big the effect of KERS will be we will know tomorrow. With no testing and no experience of this circuit, we don't know. Either we have a good surprise or a bad surprise tomorrow for all of the non-KERS cars!
"Overtaking the KERS cars is never easy, and in a place where you have more straights than anywhere else it is even harder.
Vettel, who lies 19 points off championship leader Jenson Button, believes that it is vital for Red Bull to win the race if it has the chance to do so. Although the team did not have the speed to win at Spa, Vettel is hopeful that the RB5 should be stronger at Monza.
"If it [the car] is good enough to win, then we have to win," said Vettel. "In Spa, we could not, but we had a good race and did everything that we could do. Saturday probably was not as good as we wanted it to be and we had a bad surprise like many people. Sometimes that's life.
"For Monza, we will see. It's a different circuit – higher speeds, but without the high-speed corners like at Spa."
Despite being expected to bring his eighth, and final, engine into play for this weekend's race, Vettel is not concerned about possibly not having enough engines to complete the season without taking a ninth unit, and a 10-place grid penalty.
"No, I'm not worried," he said. "Obviously it's not the best situation to be in, but you can't change it. We have to accept it and make the best of it."