Toto Wolff reveals Valtteri Bottas' retirement in Spain was due to an issue Mercedes has never experienced before.

The Finn pulled to the side of the track shortly after the battle with Sebastian Vettel that saw the Mercedes driver hold off the championship leader long enough for his teammate, Lewis Hamilton, to substantially close the gap and go on to victory.

However, the Finn retired shortly after with what was believed to be an engine failure, thus ending his 100% finishing record.

"It was painful to lose 15 valuable points with Valtteri," admits Toto Wolff. "We've identified the root cause of the problem, which was the turbo.

"We haven't seen that defect before, which shows you that you need to be double diligent," he adds. "This is a technical sport and if you stretch your limits, you'll encounter technical problems.

"We are in a massive fight with Ferrari,” he admits. “On one side, this is very exciting and challenging. But on the other side, it is going to stretch us to our limits. You cannot base your current assessment on the balance of power on just Barcelona.

"We expect Monaco to be a completely different ball game to Barcelona," he admits, looking ahead to this weekend. "The circumstances, working environment and driving challenges are completely different to anywhere else - and you need to get everything exactly right if you want to perform to your maximum around those streets. Not every factor is under your control, either, so you need to turn fortune in your favour at the right time if you want everything to come together.

"Every weekend will push us to the limit; this is the new reality of 2017. The last three years were extraordinary. But this season I have re-discovered why I love the sport. I love the intense competition. This competition means that you won't be winning easily - but that you'll have a fierce fight on your hands. Because of that, the feeling is even greater when you manage to come out on top, as we did in Spain.

"If we get the job done in Monaco, I'm pretty sure we'll bring down the garage roof. We're all properly fired up for this fight, so let's see what we can do..."