Former champions say Vettel still has something to prove

Sebastian Vettel has a big season ahead of him at Ferrari but could feel the heat from new teammate Charles Leclerc, according to retired Formula One world champions Jenson Button and Nico Rosberg.

The 31-year-old Vettel, a four-time world champion from Germany, lost out to Mercedes' Lewis Hamilton last year after making some costly mistakes that offset a strong start to the campaign.

Ferrari has brought in Leclerc, 21, as a replacement for 2007 champion Kimi Raikkonen and replaced team principal Maurizio Arrivabene with long-time insider and technical head Mattia Binotto.