Sebastian Vettel can draw on his experience and still crack a "tough nut" in Ferrari teammate Charles Leclerc.

That is the claim of ex-Formula 1 driver Gerhard Berger who was one of the key figures at Toro Rosso when the young German broke through in 2007/8.

Vettel faces a critical year in 2020, with his contract up for renewal and the pressure to respond to Leclerc, who scored more wins and finished ahead of him in the Drivers' Championship in his first season at the Scuderia.

For some, the expectation is the 32-year-old may opt to call it a day on his F1 career but the Austrian says only Vettel can make that call.

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"We don't know if it'll be a decisive year for him personally, he'll determine that himself," Berger told Germany's Auto Motor und Sport.

"Is he driving his last year and wants a good retirement? Does he want to extend his stay at Ferrari for another three years? Does he want to take Leclerc apart?

"It's clear that with Leclerc, he has a tough nut to crack but he can do it. Regardless of whether you drive a Ferrari, Mercedes or Red Bull, you always have a tough nut to crack.

"That used to be the case with the top teams. There are always two alpha animals that go head-to-head until one remains. When I went to McLaren, I had [Ayrton] Senna. You can't run away from it."

But while Leclerc appeared to get the upper hand, resulting in both drivers receiving equal status for this year, Berger thinks Seb can take heart from his end to 2019. 

"In the last third of the season, Vettel showed that he can do that [go head-to-head with Leclerc] very well," he said.

"There's no question that Leclerc has the future ahead of him and Sebastian is in the last stage of his career, but he has some insane experience, he has been world champion four times and has been with Ferrari for five years.

"From this, he can draw and balance out the boy's bravery. It will be an interesting duel, but I don't dare to predict the outcome."