Jenson Button has revealed that listening to Fernando Alonso making positive noises about Ferrari's new F10 should be a worrying sign for the Spaniard's Formula One rivals this season.

While Button already has his hands full, having opted to join fellow world champion Lewis Hamilton at McLaren for 2010, it is the upbeat demeanour of double title winner Alonso that is currently concerning him. The Spaniard, who joins Ferrari after two difficult years back at Renault, has already claimed that the F10 is the best grand prix car he has driven - notwithstanding the fact that he took two titles for the regie and came close to another in an acrimonious year alongside Hamilton at McLaren - and says that there is a lot more to come from the Prancing Horse [see story here].

For such a notorious taskmaster to appear so content with one pre-season test still to run, in Barcelona this week, is a worrying sign for Button, who told Spain's Marca that a 'happy Alonso' was likely to be a 'fast Alonso'.

The Briton will go head-to-head with his Spanish rival on the opening day of this week's group test at the Circuit de Catalunya, but knows that the results will be of little use in indicating their relative performance ahead of next month's season-opening grand prix in Bahrain. However, he remains confident that, in McLaren's MP4-25 - with which he topped the final day of testing in Jerez last week - he has a car that should allow him to remain a frontrunner.

"In 2009, I was gambling [on Brawn] and finally won, but when I saw the number one on this car, I was really excited," he admitted, "I have a feeling this is going to be the most exciting season in the history of F1."