Jenson Button admits he is surprised by McLaren's lack of pace during practice for the Malaysian Grand Prix.

Both Button and Kevin Magnussen struggled to match the top four teams over one lap at Sepang, with Mercedes, Ferrari, Red Bull and Williams closely matched. Button believes that it's the longer runs where McLaren is losing out even more and attributed the deficit to the high temperatures which were highlighting the MP4-29's weakness in high-speed corners.

"We're finding it tough out there today, especially in this heat," Button said. "We're very weak in high-speed corners so there's a lot of work needed. Hopefully the weekend is cooler than it is today - it's supposed to be for qualifying and the race - because I think we need it to be to be relatively competitive. We found it tough on the long run.

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"We can hope for cooler conditions and I think we're going to get that. The car was working better this morning in cooler conditions, so hopefully that will help us. There are a few things in terms of set-up that we need to do, but we don't have the pace right now which is a surprise actually."

And Button even went as far as to say McLaren was facing a race in the midfield based on Friday's form.

"I think our outright pace isn't there; not just compared to Mercedes but compared to half of the field really. So there is a lot that we need to do before qualifying tomorrow.

"I don't think anyone is really going to struggle with fuel management here. This is one of the easier circuits for fuel management so we don't have that advantage either!"

With McLaren running an updated nose, Button said the upgrade was not as substantial as it may appear but feels it is an improvement.

"I think it always looks bigger than it is when you change the nose box. They're going through the data still, and hopefully that has given us something. I think it probably has, which is good."