Daniel Ricciardo, running the upgraded Renault engine this weekend, ended Thursday practice six tenths up on the lead Mercedes of Lewis Hamilton.

And while practice pace isn't always representative of a team's full capabilities, Rosberg is certain Mercedes won't find six tenths just by "turning up the engine".

"It's very simple, today they were faster than us," Rosberg conceded."So we need to dig into it and see if we can find a lot of, a big chunk of laptime.

"Of course, we can still turn up our engine, but we don't have six tenths of turning up the engine, you know?

"Confident after today? No. Because Red Bull was quicker. But I am pretty confident that we can do a great job and improve the car. If it will be enough, I don't know."

Rosberg also suggested that, were qualifying to be held on Thursday, Mercedes would have suffered its first qualifying defeat since Singapore 2015.

"If today was qualifying, they would be in front of us. So we definitely need to find some more pace and it's not gonna be easy."

Hamilton says gap "very close"

Hamilton, for his part, was more optimistic than Rosberg after Thursday, suggesting the gap between Red Bull and Mercedes was "very closer".

"The Red Bulls are looking quite quick. It's close. It's not a power circuit. It's good. Now it's more exciting for the fans," Hamilton said.

"I think they are very much a threat. They are very, very fast. I don't know where six tenths is. For sure I have a little bit of time. It's very, very close."

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