Lewis Hamilton admits he has been struggling to drive his Mercedes car since joining the team this season.
qualified second for Sunday's Monaco GP,
beaten by team-mate Nico Rosberg for the third race in a row.
"I've been struggling all year. Considering it is a new car I've done pretty well, but I definitely seem to have been struggling as we've got into the season," he said.
He said he has been lacking confidence in the car during braking.
Monaco GP: Lewis Hamilton plays down victory chances
"Winter testing wasn't too bad and when we changed something in China it felt good and I got pole, so the confidence came. But that is the only race I've had that confidence, I don't know why," said Hamilton,
who joined Mercedes for 2013 after six years with McLaren.
"It is really just the uncertainty of what the brakes are going to do. I think I solved it later in qualifying so let's hope for a good race tomorrow."
Hamilton said this was the first time he had struggled in this way at Monaco, a circuit that he loves.
He said he would have liked to get pole position but "I have not deserved it this weekend. I have not been on the pace."
But he said he would still be trying to fight for victory with Rosberg.
Asked if it was every man for himself, he said: "That's how I see it. At the end of the day we want to finish one-two for the team. That is the goal.
"Of course I have to see what I can do to overtake. It's impossible to overtake here, especially when the car is equal pace. It's through pit stops that I might have a chance but I've got to make my tyres last."
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Asked about imposing team orders, team principal Ross Brawn said he would "let the race run" between the two drivers.
Team-mate Rosberg said: "This is my home and to be on pole here is fantastic. The whole weekend has gone really well. Perfect position tomorrow.
"I hope to have a good start and then our difficulties start - race pace is still our big challenge. I think we have improved things but we are coming from way back.
"Barcelona was 1.5secs slower or something. I don't think we'll be able to improve all that in two weeks, for sure not. But you can't overtake here so maybe a good result is still possible.
"It's not realistic to speak about winning at the moment because we were nowhere recently. So step by step we want to just improve."