Jenson Button admits McLaren need to find more pace over the long distance runs if they want to be competitive this weekend.
McLaren's 2014 Championship got off to a flying start in Melbourne where Kevin Magnussen and Button secured a double podium finish for the team.
It is, however, looking a different story this weekend in Malaysia.
Both Button and Magnussen battled to get inside the top ten in Friday's practice with only Button achieving the feat.
The 34-year-old's 1:40.628 was good enough for eighth place while Magnussen finished P12.
Button revealed that McLaren, whose MP4-29 is sporting a new nose tip this weekend, are finding it difficult in the heat and humidity on both the short and long runs.
"We're finding it tough out there today - especially in the heat," he said.
"We're not as strong as we'd like to be in high-speed corners - and, when you have downforce issues, they're further amplified by the hot weather. So our long runs were tricky - in terms of both tyre degradation and outright pace.
"We're now going through the data, but the upgrades we brought here seem to be giving us something - so that's encouraging - but there's a lot of work still to be done."
The Brit, who won the Malaysian Grand Prix back in 2009 on his way to the World Championship title, added that it is the long-run pace where McLaren really need to up their game.
"I'm sure people are getting excited about individual lap times, but they don't count for too much around here because you can usually overtake.
"It's the long runs that you need to analyse, and that's where we're finding it a bit more difficult."