Lewis Hamilton has admitted his defence of the world championship could stand or fall on how his McLaren fares this weekend, and the omens did not look good after he struggled in practice for the Spanish Grand Prix.

Hamilton came to the Circuit de Catalunya near Barcelona fearing that the track, which demands high levels of downforce, would expose the aerodynamic deficiencies that have caused his car to remain off the pace this year.

And those fears were realised as his time of 1.22.809 this afternoon, despite being a slight improvement on his first run-out, was still 1.2secs off the pace set by the Williams of Nico Rosberg.

Hamilton was 13th quickest in the second session, just ahead of team-mate Heikki Kovalainen, who has only scored four points this term.

Modifications to McLaren's troubled MP4-24 car during the opening four rounds of the title chase have produced results, with Hamilton claiming his best finish of the season two weeks ago when he came fourth in Bahrain.

His problem, however, is while McLaren have made strides, so has every other team up and down the pit lane. The 24-year-old said: “I guess this weekend is a good indication of whether we will be able to continue our progress. We have a couple of new things on the car, but we don't have a lot of things that are radical steps for us. It is just bit by bit we are adding stuff to the car.

“This weekend it'll be interesting to see how far everyone else has stepped forward. The difficult thing is while we progress everyone else progresses at more or less the same pace, so the key for us is to progress a bit faster.”

On today's evidence, that's just not happening. Should Hamilton fail to achieve a good points haul on Sunday, McLaren will face a difficult decision. They can plough on committing
precious resources to a car that may never be competitive, or they can effectively write this season off and instead throw everything at designing and developing a car capable of powering Hamilton back to the front of the grid in 2010.

That is what Jenson Button's team did last season. Then, as Honda, they stopped trying to improve a clearly uncompetitive car before the midway point of the year and instead concentrated on producing a car that, with Button at the wheel, has won three of the four races this year.

Although the Briton was seventh in second practice the Brawn GP man was the only driver to break the 1min 22sec barrier in the morning with his time being the third best overall.

Williams had the best of the day, though, with Kazuki Nakajima second fastest, just 0.152secs adrift of team-mate Robserg.

It is the eighth time in 14 sessions Williams has topped the timesheets but he has failed to transfer that practice pace into significant points, his best display being sixth in Australia.

Meanwhile, 1997 world champion and Indy 500 winner Jacques Villeneuve has revealed he may be lured into a Formula One comeback.

The 38-year-old Canadian, son of motor racing legend the late Gilles Villeneuve, left BMW-Sauber in 2006 but the new rules that have placed greater emphasis on driving talent rather than technical advances have rekindled his interest in the sport.

Villeneuve said: “The older drivers, those with greater experience and judgement, can better adapt to these sensitive cars. They seem fun to drive.”

A vacancy may be open with the new USGPE team, based in the United States, that is planning to join the grid next season with at least one North American driver.