An upgrade of Renault's power unit scheduled for the Canadian Grand Prix in June has been delayed indefinitely by the manufacturer.
Red Bull has confirmed the report, leaving the Milton Keynes outfit to struggle for performance behind front-runners Mercedes and Ferrari.
Red Racing Racing is still planning to introduce its 'B-spec' car next week at Barcelona but the absence of any progress on the engine front is undoubtedly a setback for Daniel Ricciardo and Max Verstappen.
Renault has apparently put its power unit updates on the backburner for reliability concerns.
"As long as Renault does not have reliability under control, there is no further development," Red Bull's Helmut Marko told Auto Motor und Sport.
"This is a setback for us."
At the same time, rumours are swirling that Renault is actually accelerating development on a single car -- the works machine raced by Nico Hulkenberg.
"The fuel may be different but the hardware is the same, Renault assures us," said Marko.
"It would be impossible to build two different engines anyway.
"You only get this impression (that Hulkenberg has a faster engine) in qualifying, but one reason could be that Hulkenberg is a frighteningly good driver in qualifying," he added.
So for now, Red Bull is putting its eggs in the 'B car' basket, with simulations promising a huge step forward of a full second per lap.
"We know all the numbers but now I want to see it on the stopwatch in Barcelona," Marko said.
Gallery: All the action from last Sunday's Russian GP
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