Montreal, Canada - Mercedes has delayed the introduction of a power unit upgrade until after this weekend's Canadian Grand Prix due to a "quality issue", a decision that also affects Williams and Force India, as well as the works team.

A spokesman for the Formula One world champion team said on Wednesday: "All Mercedes-powered cars will be running PU1 (the specification used since the start of the season) for this weekend, too, before receiving new units in France."

Mercedes team boss Toto Wolff had said earlier in the week that Mercedes planned to introduce their scheduled power unit in Montreal and were "pushing hard to bring more performance to the car as soon as possible".

Mercedes is leading both championships after six races, with Lewis Hamilton 14 points clear of Ferrari's Sebastian Vettel. Canada is one of Hamilton's favourite circuits, the one where he took his first Grand Prix win in 2007 and where he has won and started from pole position six times. If the four-times world champion wins again on Sunday he will equal Michael Schumacher's record of seven victories in Montreal.

Renault, which supplies its own team as well as McLaren and Red Bull, and Toro Rosso's partner Honda are planning to bring upgraded power units to Canada. Under the 2018 regulations, drivers are only allowed three power units per season.

Mercedes, closest rivals Ferrari and Red Bull have each won two races so far.