The extent of Nico Rosberg's career achievements in Formula 1 is not fully appreciated.

That is the view of Heikki Kovalainen, a former F1 driver who - like Rosberg - was once paired inside a team with Lewis Hamilton.

"Formula 1 is mentally and physically gruelling enough without having such a virtuoso as your teammate," he told the Finnish broadcaster MTV.

"Of the drivers who raced with Hamilton, the only one who was really able to bite into his weaknesses was Nico," Kovalainen, who now races in the Japanese Super GT series, said.

"Hamilton does have some weak points and Nico was able to attack them perfectly and shuffle the pack just enough to win the championship," he added.

"I don't think Nico's performances are appreciated as much as they should be. It's so tough to beat Hamilton with the same car, but you also have to remember that a little earlier he was also driving hard against Michael Schumacher," Kovalainen said.