Red Bull Formula 1 driver Max Verstappen has refuted Sergio Perez's claim that Renault's engine is now a match for those made by Mercedes and Ferrari.
Ahead of the Russian Grand Prix, Force India driver Perez said Mercedes-powered teams now only had an advantage over Honda.
Verstappen, whose third place in the Chinese Grand Prix is Red Bull's only podium from the first three races, dismissed this when he said he was "not sure" if engine supplier Renault was on the leaders' level.
"Of course they are working really hard," he said. "We're also working really hard to improve the car.
"But I think there is still quite a deficit. So we need to continue working hard together to make it better in the upcoming races."
Asked why he said Red Bull was braced for a difficult race at Sochi, Verstappen replied: "The power deficit on the straights.
"We are not on the same level in terms of downforce as well, so we cannot make the differences in the corners."
When the suggestion that some felt the three leading engine manufacturers were at a similar level was made, Verstappen joked: "I would like to swap one day, and then everyone talks different."
He pointed to the difference in engine performance in qualifying as one example where Mercedes still maintained a clear advantage.
"Mercedes has a mode where they can turn it up," he said.
"In the race they cannot use it as much because you can't run the engine like that the whole race.
"That's why it looks better in the race but from our side, it's more or less the same.
"We don't have this massive power mode [for qualifying]."
NO 'MAGICAL' BREAKTHROUGH IN BAHRAIN
Verstappen also revealed Red Bull still did not know why it was closer to the front in Bahrain.
Red Bull qualified more than one second adrift in Australia and China, but at the third round Daniel Ricciardo was just 0.7s behind polesitter Valtteri Bottas's Mercedes.
"It's a bit difficult to say if we really understand," said Verstappen, who added that there was "nothing special" about the Red Bull on that weekend.
"I was a bit surprised to be that much closer to them.
"In qualifying it was not a bad balance for what we could get out of the car.
"But I also had not a bad balance in China, and in Australia I don't think it was too bad.
"It's not like we suddenly found something magical that works."