Ferrari surge makes new Lewis Hamilton/Mercedes F1 deal critical

The reigning world champion's current three-year deal expires at the end of the season.

Both Wolff and Hamilton have insisted on a number of occasions over recent weeks that a deal is close but there has been no formal announcement.

Asked if it was becoming critical for Mercedes to re-sign Hamilton amid the growing threat from Ferrari, Wolff replied: "Of course, Lewis is a factor and an exceptional guy in the car.

"I think like always in life it needs to be a win-win situation and at the moment it is a win-win situation.

"We have a very quick guy in the car and we have a very quick car.

"We have a solid foundation in the team; we have built an organisation which can be successful on a sustainable basis long term.

"With Ferrari bouncing back very strongly, it's a win-win [to keep Hamilton]."

Hamilton currently leads the world championship by 27 points over team-mate Nico Rosberg following three victories from the first four grands prix of 2015.

Rosberg signed a multi-year contract extension mid-way through last season.

Shortly afterwards, Mercedes and Hamilton agreed to postpone their talks over a new deal until the 2014 championship fight was out of the way.