Mark Webber admits he is not convinced by Daniel Ricciardo's decision to move to Renault in 2019.

The Red Bull driver surprised everyone, including his fellow Australian, in announcing he will leave the Milton Keynes-based squad after five seasons for the French manufacturer at the start of the summer break.

Renault's efforts to once again become a championship-contending team was the main appeal for Ricciardo, who also cited a change of scenery, but Webber believes the risk may be a little too high.

"He's absolutely world class, we know that, he's top notch, he is one of the best on Sundays, there's no question about it," the nine-time Grand Prix told Fairfax Media.

"Let's see. I hope it's an inspired decision, we'll all have to sit back and watch, but the move is under a little bit of heat, it has to work for him.

"He knows in the short term it's going to be [a step back]. He'll be behind Red Bull next year. He's banking on the long-term there. That's the concern."

Some have also pondered if Ricciardo's decision was influenced by the rise of teammate Max Verstappen, who has out-qualified the 'Honey Badger' at every race since Monaco and outscored him 150-74 over the same period.

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Regardless, Webber's most optimistic outlook is Daniel's Renault move is a brief move back for a bigger step forward.

"That's what you've got to do sometimes, you've got to be one step back, two steps forward," he said.

"He has to be realistic about what's possible there and find out what he can realistically do with the time he's got left.

"He's got a lot of time left... but we all would like to see him in a more competitive situation than he's going to be in in the next two years."