Global Motorsport Media
Nico Rosberg has overcome a chink in his armour, Mercedes team boss Ross Brawn has revealed.
When Brawn GP became Mercedes' works team ahead of 2010, the former Williams driver was signed to be the returning Michael Schumacher's teammate.
Nearly two seasons on, despite an improved turn of form by Schumacher in the last three or four races, it is 26-year-old Rosberg who has been the faster.
But team boss Brawn did spot a weakness.
"I have to be honest, when Nico first arrived from Williams there were times when he was not fit enough," he is quoted by the Telegraph.
Rosberg has since blitzed fellow amateur triathlete Jenson Button's best time at the multi-sport discipline, and regularly posts Youtube videos proving his high fitness.
"I can't criticise him at all on that score now," admitted Brawn. "He goes above and beyond."
Brawn's praise comes amid speculation rival teams have expressed interest in Rosberg beyond his 2012 contract, with Mercedes' Norbert Haug revealing he would like to sign him up for the long term.
Rosberg says he is buoyed by the team's acquisition of well-known technical directors Aldo Costa and Geoff Willis.
Mercedes are in the background and they are pushing flat out
"Mercedes are in the background and they are pushing flat out. Whatever it takes," he said, admitting it would be special to succeed with what is effectively a German national team.
"The other thing that is special is I know that this team is betting on me; counting on me to deliver once I have the car to do so. And I'm very confident that I will be able to. I just have to be patient," said Rosberg.
"Michael, of course, isn't getting any younger. So theoretically it is all set up perfectly for me here."