Mercedes claim their data shows Red Bull are currently the quicker team after a difficult pre-season test in Bahrain.

The reigning champions completed the least laps of any team over the three days (304), as an unexpected gearbox issue after one lap on Day 1 left them playing catch up.

As the test progressed, however, concerns moved more towards the handling of the Mercedes W12, as both drivers struggled with the rear of the car.

“With the team, it has definitely been the most challenging start to a season in terms of testing,” Valtteri Bottas stated to Formula1.com after his stint on Sunday.

“Time is even more limited nowadays, so definitely not ideal. Only one-and-a-half days as a driver and for me day one was compromised. But at least I feel the recovery has been pretty good in the last two days.

"Overall the car feeling is not bad [but I’m] still not fully comfortable," he added. "We’ve been going forwards with the set-up and understanding of the car and getting it to behave better, but still there is more work to do."

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Teammate Lewis Hamilton highlighted Mercedes' lack of grip with a spin into the gravel on Day 2, albeit with some wind assistance.

And after finishing fifth on Sunday evening, the world champion admitted the team is behind on where their targets.

"I've never been a massive fan of testing, I just love racing!" he said. "But it's probably the only year I would have asked for more days though because we've got lots of work to do.

"We've never felt in the past that we were quicker than everyone else after testing because you never know what people are doing with the fuel and set-ups.

"We always just focus on understanding our car the best way we can so if I'm honest, I feel the same this year. We won't know until we get to qualifying in two weeks' time exactly where we stand.

"Today we made some improvements but it's still not where we want to be. I can't pick out any one area, it just feels globally through the lap that we need to improve.

"I'm looking forward to getting back into competition and back in that focus mode. Our team is all rowing in the same boat - we win and we lose together.

"I'm just happy to start another journey together with these boys and girls."

Of course, after so many years of Mercedes trying to downplay their performance before ultimately dominating, many are sceptical about suggestions the team are actually in trouble.

But engineering chief Andrew Shovlin is adamant the current signs show the team is not the fastest.

“We’ve made a bit of progress with the balance on higher fuel and the car was more predictable but we can see from the data we’ve collected over the last few days that on race pace, we’re not as quick as Red Bull," he said.

“The lower fuel work was a more confusing picture, we didn’t gain enough and we need to go and look at our approach as far too many cars were ahead of us on pace today.

“We’ve had issues in recent years with pace in winter testing and managed to make good progress before the first race but we may have our work cut out this time.

“We’ve not got long before we’re back here for the race so we’ve planned a programme of work to try and understand some of our issues and will be leaving no stone unturned in our efforts to find some more speed over the next 10 days.”