Jenson Button fears his title rivals may be sandbagging ahead of a crucial start to the European season.
Championship leader Button finished Friday's practice ahead of Sunday's Spanish Grand Prix with the fourth quickest time, despite conceding to a balance issue with his Brawn GP car.
It has long been expected the major players in Formula One would rise again at Barcelona's Circuit de Catalunya following troubled starts to their year during the flyaway races.
However, Ferrari, McLaren and BMW all suggested their times of strife are not yet over, leaving Button to again battle with the likes of Red Bull Racing, Toyota, and potentially even Williams.
The 29-year-old, though, remains sceptical about the performance of the big boys as he said: "Ferrari were quite good in the morning.
"Teams might be playing games, a lot of people do on Fridays. We've done it before. We will wait and see.
"If you look at the consistency of the cars, you would say the Toyotas and the Red Bulls are competitive - the others I haven't really paid that much attention to."
After winning three of the opening four races to open up a 12-point cushion over team-mate Rubens Barrichello, Button is refusing to let his focus waver, despite natural exuberance at his position.
"I'm enjoying leading the way - although not being the centre of attention," smiled the Briton.
"It's obvious I've been quite happy with the way the first four races have gone, winning three out of four, winning every single dry race has been pretty exceptional and very enjoyable.
"But you have to look to the next race - that's the way it is - because they come and go very quickly.
"Every race I go to I'm thinking about how well I can do over that weekend. I'm not even really thinking about Sunday.
"It's just lap by lap, gaining as much information as we can throughout the day and not thinking too far ahead.
"We also know there is a long way to go this year. Brazil and Abu Dhabi are a long way away, and we have to do well in all the races."
It was a different story for World Champion Lewis Hamilton, though, as he endured a torrid day in his McLaren, prompting a terse Q&A session after he had stepped out of the car.
A stern Hamilton snapped that there had been "no improvement to the car whatsoever," and that he would battling at the back of the grid on Sunday, not at the front like in Bahrain a fortnight ago when he finished fourth.
Hamilton also insisted there was no sandbagging from his team, adding: "I wish we were, but we are not.
"We are pushing, but unfortunately we tried some upgrades and they are not working for me.
"From what I've experienced in practice, we definitely have a few problems."
At least there was a touch of defiance at the end as he concluded: "We will still battle our way through."
