Mercedes team boss Ross Brawn says the W02's problems have been exacerbated by short-notice changes made to resolve a cooling issue.
But he remains adamant that the definitive 2011 package that will be ready for the final test will both tackle this problem and bring Mercedes fully up to speed.
Mercedes' form has been disappointing for much of winter testing so far, though the team and drivers insisted that this was because of a tactical decision to launch with a 'basic' design to perfect reliability before bringing the final 2011 specification car to the last test.
Now Brawn has admitted that some of the lack of speed has been down to changes made necessary by the cooling worries.
Asked, in an interview for the team's official website, if he was worried that Mercedes appeared to be trailing the leaders, Brawn replied: "It's a fair statement. We are well aware of the pace of our current car, the distance to the current frontrunners and the reasons for this, which include the compromises brought about by our cooling issues.
"Our intention was always to launch the car in a fairly basic specification to allow more time to focus on the upgrade package. This inevitably means that we look further off the pace than people might expect.
"Knowing all of the facts, I am comfortable with our current position and the developments that we have to come."
He said the temporary solution to the cooling issue had been a significant performance limitation.
"The biggest challenge for us so far has been a cooling problem," Brawn acknowledged.
"The short-term modifications that we made to the launch-specification car cost a reasonable amount of performance.
"The solution has been incorporated into the bodywork design for our upgrade package and will recover that performance before the first race."
He added that while Mercedes' reliability had not been flawless, he was content with that aspect of its preparations.
"You naturally expect to experience faults with a new car and fortunately we've had relatively few of a 'car-stopping' nature so the impact on our programme has not been significant," said Brawn.
"Our mileage has been good, we've covered 4,300kms over the three tests to date and, of course, the more mileage you can achieve, the more opportunities there are to identify any issues and resolve them before the season gets underway."