Mercedes boss Toto Wolff says it is up to his team to "react" at the Bahrain Grand Prix after a tricky pre-season.

The reigning champions completed the least laps of any team across the three days of running two weeks ago as questions over reliability and then the handling of their 2021 car were raised.

Of course, most are sceptical about any suggestions Mercedes start the new season behind, but Wolff insists the issues are genuine.

"We've had some great performances over the years and that is why everyone is saying that we are sandbagging," he told Austrian broadcaster ORF.

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"I think that we were the team that was running with the most fuel, but regardless, the car was a bit toxic to drive and fairly unstable, especially with the crosswind.

"It seems like we have a small diva, like the car from two years ago, that we haven't really understood yet."

By contrast, expected rivals Red Bull enjoyed a smooth test and appear to have made good gains from last year. 

"Red Bull looked strong on both the long and the short runs, but as always with testing, it's difficult to be certain of true performance," Wolff added.

"The only thing we know for sure is that we must prove our ability to react. From the moment the third day of testing finished, we got our heads down and started to figure out how we can return to Bahrain in stronger form in just a few days' time."

Red Bull though believe Mercedes will have little problem in once again asserting themselves as the team to beat.

“There is no denying that after the smooth running of the three-day test in Bahrain, there seems to be an excitement out there that we can end Mercedes’ seven-year dominance of F1,” said team boss Christian Horner.

“But we had a debrief within the team after the test and it is fair to say we are a little more cautious on the subject and we cannot underestimate the size of the challenge ahead of us on many fronts.

“We know that Mercedes has not won by mistake for the past seven years; they are a quality, class team that will be motivated to come back strong.

“We saw it a couple of years ago where there was a similar story during pre-season testing and then they smashed it out of the park at the first race in Melbourne.

“So, you cannot take anything for granted and at this stage, it is good that we have a solid basis from which to develop the car, rather than fixing an inherent problem.

“Of course, Mercedes are trying to move the spotlight away from themselves, which is all part of the game, but the reality is they are the reigning seven-time world champions and it is down to us to close that gap and put up a fight.

“They had one of their strongest seasons last year and this year’s car is an evolution of that, so let’s see what we all have in Bahrain and the rest will follow.”