Jerez F1 test: Nico Rosberg says Ferrari's early pace is eye-opening

Nico Rosberg has described the performance of the Ferrari team as "an eye-opener" after the opening three days of Formula 1 testing at Jerez.

While the German is satisfied with the progress his Mercedes team has made in terms of racking up the mileage, having completed a further 151 laps on Tuesday, and is confident of being in good shape, he singled out Ferrari as a team to watch.

"We are keeping an eye on the opposition, especially Ferrari has been an eye-opener in the last couple of days," he said.

"But still we are confident that we can start the season well and in terms of development be strong."

Rosberg ended the day third fastest, behind Felipe Nasr's Saber and Kim Raikkonen's Ferrari and admitted to suffering from a telemetry problem during the day.

He also caused a red flag after stopping on track after a "fuel-pressure" problem while on an in-lap, likely to be an out-of-fuel run.

But Mercedes has still completed 1098 miles over the three days of running, significantly further than what second-best Sauber has managed with 743 miles.

"Last year, our weakness was reliability, so we focus on that," he said.

"It's important to see the problems when you still have time before Melbourne.

"The problems you see in Barcelona [where the next two tests are held], time is going to be short so it will be more difficult to solve them.

"Anything you find here is going to be much easier [to fix] and that's why it's so important to try and get the miles done.

"It was good because we did find some weaknesses on the car and they are going to be easy to fix, so we are going to be on the right track."

Red Bull Racing's Daniel Ricciardo echoed Rosberg's comments regarding Ferrari, praising the early form of the SF15-T.

"The time Seb [Vettel] did yesterday was quick," he said when asked which team he thought was closest to Mercedes.

"I don't know about fuel and tyres or whatever, but it was a good time.

"Ferrari looks good for now."