Mercedes will not be bringing new upgraded power units to the Canadian Grand Prix this weekend after all.
The manufacturer blamed a last minute "quality issue" as the reason for the change, which also affects customer teams Force India and Williams.
Montreal is the seventh Grand Prix of the 21-race season, making it the right time for Mercedes to introduce the second of the three allowed units for 2018.
A fresh engine would have meant a welcome boost in power at Canada's Circuit Gilles Villeneuve, which is characterised by its long straights.
The original power unit would have been held back and used again in Hungary where the tight and twisty circuit would have made the power differential less of a factor.
But on Wednesday, Mercedes was forced to announce that its plans had been changed at the last minute.
“Although we had hoped to introduce PU2 this weekend, a quality issue means that this has now been delayed by one race," said a team spokesperson.
"All Mercedes-powered cars will be running PU1 for this weekend," the spokesperson added before confirming that the new power unit will be rolled out for the next race in France in two weeks time.
Mercedes boss Toto Wolff previously said earlier this week that the team was “pushing hard to bring more performance to the car as soon as possible.”
Ferrari is still expected to be giving new engines to Sebastian Vettel and Kimi Raikkonen this weekend. However, this has not yet been officially confirmed.
Renault has been on a more cautious development program, but is still expected to upgrade its units in Montreal for at least some of its drivers. However, new parts on Daniel Ricciardo's car means that the Australian will have a big grid penalty for this weekend's race.
Both Pierre Gasly and Brendon Hartley will have new Honda units in their Toro Rosso STR13 cars.
"We are introducing an updated PU for this event, fitting it to both cars," Honda's technical boss Toyoharu Tanabe confirmed. "The updates are mainly to the ICE, focusing on improving performance."
The lack of a new power unit could put Lewis Hamilton on a back foot. He has won and started from pole position six times in the past and was relying on this weekend's race to help him pull out a bigger lead in the drivers championship.
Hamilton's margin over Vettel in the standings is currently just 14 points.
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