HOCKENHEIM, Germany - With Nico Rosberg all signed up for the future, Mercedes' attention is now turning to the occupant of its other silver seat.Toto Wolff told Kronen Zeitung, Austria's biggest newspaper: "Yes. We are already sitting together and negotiating with Lewis Hamilton - about a multi-year contract, even." Wolff said Mercedes is more than happy with its current driver line-up of Rosberg alongside Hamilton.'WE HAVE DIFFICULT MOMENTS'Wolff said: "Lewis is a fixed part of the team and I would hope for a long time to come."For the moment, however, Hamilton is keeping a low profile on the subject. There are paddock rumours he might be tempted to return to McLaren, particularly if Rosberg goes on to win the No.'1' for his 2015 car.Hamilton said: "My contract ends in a year so I have time. I'm not thinking a great deal about it."Even Rosberg seems happy for Hamilton to stay, even though they have clashed off the track this year as they fight for the drivers' title: "I see no reason why it can't work as it has in the long term."We have difficult moments but then we discuss them together and move on.Stay with Wheels24 for the 2014 F1 season – fresh reports every day.