The 2008 world champion left McLaren ahead of the 2013 Formula 1 season to join Mercedes, who have only won one Grand Prix since returning to the sport in 2010.
The 28-year-old told Sky Sports News: "Right now I'd definitely take a third, I think it would be a massive positive for the team and would be a very good starting step for us.
"It would be wrong of me to say that we don't want to win the World Championship this year. Every guy or girl that's working flat out at the factory wants us to win, they want us to succeed this year, as do I.
"It's going to take some time and if it means that we build a foundation this year, and then we have a chance to win it next year, then great. If we have a chance of winning at some point this year then that's going to be a bonus for us"
The first race of the season takes place in Melbourne next weekend.