Formula One™ supremo Bernie Ecclestone has delivered a scathing assessment of Nico Rosberg's star potential, claiming it is nothing compared to Mercedes stable-mate Lewis Hamilton's.

Rosberg led the drivers' championship for much of 2014, but a late charge from Hamilton saw the Briton add a second title to the one he won in 2008.

Hamilton, often seen as the 'racier' of the team-mates, and Rosberg clashed on numerous times last season, going wheel-to-wheel memorably in Bahrain and Belgium.

But, in a conversation between Ecclestone and Rosberg on F1™'s official website, the 84-year-old was unrelenting in letting the German exactly what he thought of him.

"When it comes to F1™, I am a huge Lewis fan because he is a super promoter of the sport," Ecclestone said. 

"From a pure business aspect - sorry Nico if I have to say this - you are not so good for my business."

Rosberg replied: "Wait a minute. That is a hard call."

But Ecclestone went on: "Unfortunately you don't have the German fans on your side. 

"As the cancellation of the German Grand Prix™ indicates, Germany is a terrible market for Formula One™. 

"On the contrary Lewis is a hero in the UK. The British love Formula One™. Sebastian [Vettel] is also not doing much for F1™. People hardly recognize him on the street."

The German Grand Prix™ is absent from this year's F1™ calendar due to the Nurburgring's new owners being unable to stump up the entry fee demanded by Ecclestone.

Reports have suggested the iconic Italian grand Prix™ at Monza could follow suit as costs continue to skyrocket in the sport.