Nico Rosberg fears the threat from Ferrari in this weekend's Bahrain Grand Prix, describing their pace as 'dangerous' and 'worrying'.
Following Friday practice, in particular the evening session under the lights at the Bahrain International Circuit, Mercedes appeared comfortable.
Rosberg topped the timesheet with a lap of one minute 34.647secs, finishing 0.115secs quicker than team-mate Lewis Hamilton after the reigning champion locked up in the second sector, costing him four tenths of a second.
Ferrari duo Kimi Raikkonen and Sebastian Vettel finished third and fourth quickest, just over half a second adrift of Rosberg.
Yet the 29-year-old German, who trails Hamilton by 17 points in the drivers' standings, is deeply concerned by Ferrari from what he witnessed over the course of the two 90-minute sessions.
"We are very quick on one lap again, and Ferrari are very dangerous on the long run," said Rosberg.
"They have serious pace, which is very worrying. It looks like they are a genuine threat.
"In qualifying we are much quicker, but in the race they are quick.
"Tyre wise, it is pretty straightforward, with both tyres (the soft and medium-compound Pirellis) quite robust. It is just the absolute pace which is important."
Barring mistakes it appears another Mercedes front-row lock-out is likely, with the Ferraris occupying the second row, and from there a battle with strategy and pace.
Hamilton has also expressed concerns about Ferrari as he said: "They are going to be very close. They look very good, from what I can see, in the long run.
"The crucial part is we know we have speed in a qualifying lap, so it's more the speed on the race runs.
"That's an area we're really trying to work on, but other than that the car has been feeling very good, I'm really happy with it."
Vettel, 13 points adrift of Hamilton, endured a disruptive day as a loss of power compromised FP1, whilst a collision with Sergio Perez in his Force India hampered FP2.
McLaren's Jenson Button also suffered a wretched day with technical issues in both sessions, resulting in a lack of running that left him down in 19th position, 4.5 seconds behind Rosberg and sandwiched between Manor duo Will Stevens and Roberto Merhi.
Saturday could be problematic for all, though, as a sandstorm has been forecast to hit the area at some point during the day.
Source: PA
