Fernando Alonso says Friday's practice for the Australian Grand Prix has revealed nothing about the true pace of the teams.
Although Red Bull topped the first session, it was McLaren which finished on top in the afternoon, with Jenson Button leading team-mate Lewis Hamilton.
Ferrari driver Alonso, third quickest, said the real pace of the cars has not been seen yet.
"Nothing new yet and what else would you expect? These two free practice sessions have not actually revealed the real relative strengths of the teams," said Alonso.
"This morning Red Bull went well and in the afternoon it was McLaren's turn, with us and Mercedes always in the mix, while Williams and Renault also seem competitive.
"There are so many teams who could be in with a chance of going for the win and therefore it's obvious that it will be necessary to have a good Saturday, without any mistakes if you want to start from the front row.
The Spanish driver insisted the performance of Pirelli's tyres was still a bit of an unknown, and reckons a flexible strategy will be a must in the race.
"We will need to be very flexible during the race, because at the moment, we know too little about the tyres to be able to say with certainty on which lap it will be best to stop. From what we have seen today, maybe we can do ten laps on one set of tyres, or maybe thirty!
"I am happy with the way the car is going: at the start there was a bit of understeer and we still are a way off from having perfect grip at the front, but it went better than I was expecting."
Team-mate Felipe Massa posted the seventh quickest time, and the Brazilian also made it clear that the behaviour of the tyres was still hard to predict.
"From what we have seen, the soft tyre shows less degradation than we might have expected, but we have to work out if that will still be the case in the race," he said. "This track is definitely less hard on tyres than Barcelona for example, where we did so much testing.
"This year it will be vital to study their behaviour carefully, circuit by circuit. The difference in outright performance between the two types of tyre is very marked. McLaren and Red Bull seem very strong, but there are other cars that can also be on the pace."