Nico Rosberg has said that four years with the Williams team 'wasn't ideal' although the German driver says he doesn't regret the way his career has panned out so far.

Despite the fact he has now completed six seasons in the sport and started over 100 races, Rosberg has yet to secure a breakthrough victory, with the past two seasons having failed to match expectations with Mercedes.

Prior to that, Rosberg endured a frustrating spell with Williams as the team was unable to repeat past successes and having missed out on the chance to move elsewhere during his time with the Grove-based team, Rosberg admitted it hasn't been ideal to spend four years with Frank Williams' outfit.

"There was the interest, but Frank (Williams) would not let me go," he told Auto Motor und Sport. "Certainly being four years at Williams was not ideal - it could have been a bit shorter. But particularly the last season there was a springboard for me.

"Since then I have been always seventh in the standings and made some others aware of me.

"I have no regrets. I am completely convinced it was right to go to Mercedes and to stay here."

Rosberg extended his deal with Mercedes last year.