Lewis Hamilton says he expects a "tough battle" for his Mercedes team in the Bahrain Grand Prix.
Hamilton was 10th fastest in second practice on Friday, 0.822 seconds off pace-setter Kimi Raikkonen's Lotus.
"I don't think we are as far off as it looks. I think other people were on different fuel loads," he said.
"It looks like we're 0.6 seconds off the pace. I think it's maybe half that; maybe a bit less. But it will be a tough battle for sure this weekend."
But he said there was little chance of him repeating that performance in Bahrain.
"It's not looking like that at the moment," he said.
Ferrari, Lotus and Red Bull appear to be the most competitive and set for a close battle in the race.
He said he believed the team might have made a mistake with the set-up of his car.
"We had some problems in P1 [first practice] with the car so I was really struggling with the balance," he said.
"We made some changes and it improved for the second session but in terms of pace we were struggling, the balance is not really where I want it to be so we have a lot of work to do tonight."
Asked why the car was off the pace, he said: "I don't know, I'm literally just about to go and ask my engineers that.
"They have changed settings to what they think the track needs but I'm not convinced that's the right way to go.
"I don't know whether they're right or wrong but we are struggling a little on pace today. But I'm sure we'll find it from somewhere."
McLaren's Jenson Button, who was 11th fastest, said he was also expecting to struggle in Bahrain.
"Traction is probably the weakest part of our car and I think everyone knows that. It's a big traction circuit so it's a bit tricky for us," he said.