The French manufacturer, which supplies Toro Rosso and Red Bull, has come in for a lot of criticism so far this season, with its engine behind Mercedes and Ferrari in terms of performance.

Red Bull boss Christian Horner said Renault was in "a bit of a mess" after two engine failures at the Australian Grand Prix, while the French manufacturer has since threatened to quit the sport.

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However, in Malaysia, Red Bull said the Renault power unit had improved since Australia and Toro Rosso is in agreement.

"I have to say Renault has made a massive step compared to Melbourne," Key told AUTOSPORT. "There were issues at Melbourne that affected us.

"There was some driveability issues and so on but it has done a really good effort to give us something in Malaysia that the drivers are really happy with.

"It's still not perfect, but it's a lot better than the first race.

"We need that performance because Ferrari has made that step forward and Mercedes are strong.

"But I think after a tricky weekend in Melbourne, Renault has recovered very effectively."

Toro Rosso's Max Verstappen and Carlos Sainz Jr finished seventh and eighth in Malaysia, leading home the Red Bulls of Daniil Kvyat and Daniel Ricciardo.

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