Nico Rosberg says Ferrari's long run pace from Friday practice in Bahrain is "very worrying" for Mercedes.

Rosberg topped FP2 as Mercedes maintained its clear one-lap advantage over Ferrari, but it was the long runs in the evening session which were of most interest. There was very little to choose between Mercedes and Ferrari's lap times and Rosberg says that is a big concern.

"It was a good day today, obviously lunchtime [FP1] was a bit useless because it's so hot and the race is in the evening, so we didn't learn much and that's why this evening when the temperature went down again it was important to do many laps," Rosberg said. "It was good but the pace of the Ferraris is very worrying because in qualifying we are again much quicker, but in the race [simulation] they are quick."

When asked directly if Ferrari is a genuine threat for a race win, Rosberg replied: "Yeah, for sure. It looks like it."

He was also asked if he had been focusing solely on qualifying set-up, to which he said: "No, definitely not because the race is where it is going to be decided. Here you can overtake on this track, so you've got to have the race set-up nailed."

With qualifying and the race due to be run under floodlights Rosberg also questioned the timing of FP1, run in unrepresentative conditions at 2pm local time.

"We've learned that it is pointless driving at lunchtime because we don't learn anything because the race is in the evening and it's such different conditions. After that in the evening we learned that we were very quick on one lap again and the Ferrari is very dangerous to us on the long run because they have serious pace."