American motorsport legend Mario Andretti admits he is unsure if 2019 is the "right moment" for Charles Leclerc to join Ferrari.

At 21, the Monegasque will become the youngest driver in over half a century to race for the Scuderia this season and the least experienced since Gilles Villeneuve moved from McLaren after just one race in Formula 1 in 1977.

While expectations are high for Leclerc to continue his meteoric rise, Andretti expressed caution believing Charles may end up playing a support role to his new teammate Sebastian Vettel.

"The Leclerc-Vettel pairing seems correct, the alternative would have been to continue with Kimi because he and Sebastian got along very well, but we will see," he told Sky Italia.

"Leclerc seems to be very good and being young means he has a good future ahead of him. It was [former chairman Sergio] Marchionne’s idea to promote him but I don’t know if this is the right moment for Leclerc.

"With two drivers in a team, there must be a number one and a number two, having two number ones never works."

The 1978 world champion would throw his support behind Vettel, however, despite the German being criticised for a number of errors that contributed to another failed championship bid last year.

"He is absolutely the right man for Ferrari," Andretti declared. "I remember in his first year with Red Bull, I asked him what were his ambitions for the future and he immediately replied: Drive for Ferrari!

"He is the right driver for the job. I think it’s hard to say who between [Lewis] Hamilton and Vettel is better because they drive different cars, but they’re both good guys."

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Finally, Andretti also backed the Italian team's decision to axe Maurizio Arrivabene as team boss on Monday, and replace him with technical director Mattia Binotto.

"It doesn’t surprise me so much because there has always been a policy there: if they don’t win, someone has to leave," he said.

"We saw what happened to Stefano Domenicali, who was great there… the team principal is always to blame.

"Ferrari must always be at the top because this serves to keep interest alive. Nobody works harder than Ferrari, because there you breathe and you live for Formula 1."