Mercedes' Lewis Hamilton leads Ferrari driver Sebastian Vettel by 14 points heading into Sunday's race at the Circuit Gilles Villeneuve

Lewis Hamilton is concerned he will have a "difficult weekend" at the Canadian Grand Prix following the postponement of an engine upgrade.

Mercedes have said "quality issues" mean that the team's second-generation 2018 power-unit will be used at the subsequent race in France instead.

Rivals Ferrari and Red Bull both have engine upgrades for Montreal.

"If the others are bringing upgrades and have fresh engines, we won't be in a position to fight," said Hamilton.

"It is a power circuit. There is power loss over the life of an engine. All I am hoping for is reliability.

"If I am on the seventh race, with a power difficult circuit, I just want to see it through. Naturally I am still here to win.

"But they have upgraded engines, which can be from 0.1-0.2 seconds. Ferrari are very strong on the straights. It will be interesting to see whether we can match them or not, but we are going to be giving it everything we've got."

Hamilton is 14 points ahead of Ferrari's Sebastian Vettel in the championship heading into the weekend in Montreal.

Mercedes found a problem with the new specification engine in testing prior to Canada and decided they had to delay its introduction.

The engines being used in Canada are not out of mileage - they were previously scheduled to be run at the Hungarian Grand Prix at the and of July.

But engine power is less important in overall performance at the Hungaroring than at the Circuit Gilles Villeneuve.

And Hamilton will now race at a circuit where power is important with an engine towards the end of its life.

"It definitely was our target but the guys worked as hard as they could and had to take a sensible decision to not bring it here, which is definitely unfortunate, but it will mean our performance is not really the greatest," Hamilton said.

"It will be the seventh race on the engine. The goal is to make the engine stay the same all the way through, but naturally it is degraded, you lose brake horse power over races and if we're in the 7-8,000km or whatever it is, it will definitely have lost performance so at a power circuit it will probably be magnified."

Mercedes' decision affects all of its teams and drivers, so in addition to factory drivers Hamilton and Valtteri, Force India's Sergio Perez and Esteban Ocon and Williams' Lance Stroll and Sergey Sirotkin will also stick with the engines they have been using since the start of the season.

Rival engine manufacturers Ferrari, Renault and Honda are pressing ahead with planned power-unit upgrades this weekend.

However, not all the drivers from the Renault-engined Red Bull, Renault and McLaren teams may get the upgrade, depending on how taking it would affect their closeness to penalties for excessive engine usage.

Red Bull technical director Adrian Newey said earlier this week that Daniel Ricciardo, third in the championship, would receive a grid penalty of at least 10 places this weekend as a result of new parts required following an engine problem that afflicted the Australian on his way to victory at the last race in Monaco.

Newey said the Renault upgrade was worth about 0.1 seconds a lap.

Both Toro Rosso drivers, Pierre Gasly and Brendon Hartley, will have an upgraded Honda engine.