Jenson Button says he is expecting a challenging race for McLaren after admitting he was "a long way off" in Friday practice for the Japanese Grand Prix.
Button ended the day 16th fastest, as teammate Fernando Alonso -- who is running an upgraded engine for Honda's home race -- was eighth. The 2009 world champion says McLaren's race pace is his greatest concern, while he also suspects he could have a problem on his car.
"The long runs are a big issue that we need to solve," Button said. "Normally that's my forte, but today it wasn't, we're a long way off. We're looking into the reasons, to see if there was something wrong with the car or not.
"Fernando had some slightly different bits on his car but even so we should have been more competitive in the long runs and not way off. I think there are some things we need to look into. I think there's something wrong rather than a set-up issue, so we have to get that right for tomorrow."
Although he expected to be higher up the order, the Briton remains optimistic about McLaren's pace over one-lap and reckons the Woking-based outfit could challenge for a place in the top 10 during qualifying on Saturday.
"Our one-lap pace wasn't too bad but I just didn't get a great lap in. it's actually very close, between 7th and where I am, 16th, just 0,4s. If we get a good lap tomorrow, I think we could be popping into the top ten, which would be great."
The 2011 Japanese Grand Prix winner confessed he is hoping for rain in Suzuka, believing it will provide McLaren with the team's best chance to record a strong result.
"I'd love it to rain; it's the only chance we have to get a big result here. If it's dry, as long as we get everything together tomorrow, we can still get into the top ten. Then, as I said, degradation is massive, although I can get the tyres to work well over the first lap. That's why I think there's something wrong in my car."