Nico Rosberg says he is expecting a difficult Abu Dhabi Grand Prix after having to revert to an old engine for the remainder of the weekend.
The Mercedes driver topped the times in second practice on Friday, but revealed he is using an "extremely old" power unit that is hindering his performance on the straights.
Rosberg outpaced teammate Lewis Hamilton in the evening session, but he believes the Briton was not showing his real pace.
"It has been a good start to the weekend, even though Lewis did not show his pace on one lap," said Rosberg.
"It is clear that he still has some reserve. Today is not the real picture.
"In general it is going to be difficult because I have an extremely old engine, as I lost my fourth engine of the year, and the one I have has a lot of miles on and that is costing me straightline speed.
"So it is going to be a difficult weekend as a result. I just have to go quicker in the corners."
The winner of the last two races added: "I am just always slower on the straights the whole weekend as I have very, very high mileage," he said. "And it is very old the engine – and this track is an engine track.
"In Brazil it was difficult and the race before, but here is the ultimate engine track so it costs more laptime. But it is what it is, we just have to do our best."