Mercedes GP are unlikely to build a Championship-winning car this year, according to Michael Schumacher.
The seven-time World Champion feels the Brackley-based squad are still lagging behind, and also warns it will take time to get back to the front.
"Realistically, I don't think we can achieve a Championship car from where we started last year," he said.
"We have to build our way there, and I'm confident we can do that in the future, but let's take it step by step."
Although cautious about the team's chances, Schumacher promises that he will give it his all in the battle for the Championship this year.
"I am still around to fight for the Championship. Absolutely. Whether we can do it or not is something that will be proven this year."
While most of the front-runners have started the first pre-season test with their new challengers, Merc are running a 2011-spec car in Jerez, and word in the paddock suggest they are trying to "hide a clever new front wing" from their rivals.
Schumacher, though, still managed to top the timesheets on day two as he was the only driver to dip under the 1:18 mark.
"We had a productive day. We did a lot of mileage, not just cruising around," said the 43-year-old.
"We did some very good work with the new tyres that we have to face this year. That was the main focus for us.
"We used the old car and know what the difference is between this year's and last year's car, trying to understand a programme.
"The tyres have changed quite a bit. Certainly they are more consistent and a lot closer to a Formula One tyre as you would expect, and what you would wish to have.
"Therefore I'm quite happy for Pirelli to have developed this well. I had a good day yesterday and today, and for a race driver that is important."
Asked as to his concerns at being four days behind the other teams, he replied: "The main point is the reliability factor.
"If the car has a certain performance it will be reasonably quick, unless you have unexpected circumstances, which we have had in the past.
"We hope not to have these again, to have learned our lesson, with our programme done in a way that we believe in it."
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