Former Red Bull team mates Mark Webber and David Coulthard believe the jury is still out on whether Mercedes' Valtteri Bottas has the ability to challenge team mate Lewis Hamilton.

The Finn isn't exactly an unknown quantity in Formula 1 but the lack of a winning car in his four-year career makes evaluating his true potential a difficult exercise.

"We don’t really know much about Bottas," Coulthard told the Daily Mail.

"We know he’s talented, Finnish and capable of answering questions in a nice, polite way but it would be great if we had friction between him and Lewis.

"Lewis isn’t fazed by any of his team-mates because he knows he has that speed advantage.

"He has said he gets along well with Bottas which probably means he hasn’t been challenged by him in the engineering office or seen anything on the data that scares him.

"The evidence of Bottas at Williams suggests he’s not at Hamilton’s level, but maybe Bottas is suddenly going to appear as this winning machine that nobody saw coming."

Aussie Mark Webber seems equally unsure of what Bottas can deliver. While hoping for a broadening of the fight at the top, the former F1 winner and WEC champion believes the title will ultimately be disputed by Lewis Hamilton, Sebastian Vettel, Daniel Ricciardo and Max Verstappen.

"First of all, I am sorry that the reigning world champion is not with us," Webber said.

"Nico Rosberg has chosen to enjoy his family, friends and all the fun in life that Formula1 can't offer. I myself now lead such a life and it's fine.

"The title fight will go in 2017 between Hamilton, Vettel. Ricciardo and Verstappen. Bottas I'm not completely sure is ready for the title."

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