Button expects strong Ferrari challenge

Ferrari set top five times in the first session but fell into the midfield later on.

Instead Brawn, Williams and Toyota - the three teams at the centre of the diffuser row - led the way, but Button still expects Ferrari to be a threat.

"This morning they weren't (slow)," he said. "The long run of (Felipe) Massa on the prime (tyre) wasn't too bad. He was probably one of the quickest on his long run pace.

"I don't think they're slow and we've seen in the past the Ferraris and McLarens don't give their maximum. We'll see tomorrow morning."

He denied that the three teams with the alternative diffusers were set to dominate.

"You have to say that Ferrari are looking quick as well," Button insisted. "I didn't really look at the times really. I saw one long run time from Toyota and one from Felipe. I don't know who's competitive.

"The Williams has put in some good lap times - I don't know where that's come from, but we're just getting on with our job at the moment."

Button added that while Brawn was already on the pace, there was much more to come from his team once it addressed some balance issues.

"The pace is reasonably good and that's on the long runs on the tyres which is good," he said. "But there are still a lot of areas we need to improve - we're nowhere near sorted yet."