Canadian Grand Prix: Lewis Hamilton says he can overhaul Sebastian Vettel in 2017

Sebastian Vettel has extended his championship lead over Mercedes' Lewis Hamilton to 25 points

Lewis Hamilton admits it will be difficult to overhaul the advantage his rival Sebastian Vettel of Ferrari has in the World Championship this season.

Vettel has won three of this year's six races and leads by 25 points heading into Sunday's Canadian Grand Prix.

Hamilton said: "It is going to take a lot for us to catch those points up but so much can happen in the season.

"There are 14 races left. It's too early to say we're on the back foot - it is so early in the season."

Hamilton added: "We are just not in our most comfortable position, but it doesn't mean we can't fight and win the championship. It just means it will be harder for us to do so than perhaps the others."

Montreal is one of Hamilton's favourite circuit and he has won five times in nine races in Canada but he said he did not regard this weekend as a must-win.

"If we don't win here, we have 13 races more to win," he said. "If we don't win here, we will focus hard to win the next one.

"This is just one circuit that has its own unique characteristics. Other circuits, with higher downforce, we have done well in Barcelona and China so there will be races where we are strong and perhaps not. We are going to try to make sure the car is quick everywhere."

Form guide: Hamilton and Vettel's progress so far

Mercedes have been struggling to make their car work consistently, and are suffering particular problems getting the Pirelli tyres into their operating window.

This contributed to a difficult weekend at the last race in Monaco, where Hamilton qualified 14th and finished seventh.

Canada has similar characteristics, in that it has a low-grip, low-abrasion surface and lots of slow corners.

Hamilton said: "We are working hard to rectify the issues we had in the last race and we will attack this race. We have some unique bits on the car this weekend and it doesn't mean we can't take the fight to them."

Vettel said: "If it turns out to be a good weekend for us here, great, but it is a long year, the cars will change, there will be big updates coming, so important to stay there.

"At this point of the year I am not really bothered by the championship. We need to collect points, and if you win a lot of races you score a lot of points. Then later in the year we can be a bit more sophisticated."