Mark Webber says the next few days will be critical for Red Bull as they prepare for this month’s Formula One season-opening race in Melbourne.

The world champion team were fourth fastest in testing at the Catalunya circuit in Barcelona with Webber behind the wheel.

“It’s starting to build up for the first race and we’re pretty excited … however, we still have plenty to go through this week,” Webber said.

“We certainly have a few more boxes to tick. We have some crucial data to gather this week and the next three days will be really important.

“We’re learning every run and we are making progress I think.”

Lotus-Renault’s French driver Romain Grosjean posted the fastest lap on the first day of final testing.

Grosjean clocked a best time of 1min 23.252sec, a turnaround for the team which was forced to skip the first week of testing last month because of a problem with the car’s chassis.

“We lost some days last week, now we have to work twice as hard to get back those days and hopefully the car is good straight from the beginning,” Grosjean said.

He bettered the time set by McLaren’s Jenson Button in the opening session of 1:23.510.

McClaren team manager David Redding said that after running more than 2000km at Barcelona last week “today was always going to be more about quality than quantity.”

“We wanted to drill a little deeper into our understanding of the car, and that meant undertaking some bigger set-up changes that wouldn’t ordinarily be available to us during a grand prix weekend,” Redding said.

Ferrari had a low-key session, Felipe Massa coming in eighth as the team get to grips with their new car.

Two of the 12 F1 teams – HRT and Marussia, who raced as Virgin last year – were absent again.

HRT are hoping to have their car ready for a run out on the final day’s testing on Sunday, while Marussia will not be able to trial at all after failing a mandatory crash test.