Charles Leclerc's Ferrari "honeymoon" is over and he must challenge for the Formula 1 championship in 2020.

Last year, Leclerc made his impact primarily in qualifying by leading the way with seven pole positions but also showed his racecraft in brilliant battles with Max Verstappen and Lewis Hamilton, winning twice.

But as 2009 world champion Jenson Button looks ahead to this year, he sees a crucial year for the Monegasque as he evolves from up and coming youngster to trying to prove why he should lead the most iconic team on the grid into the future.

“Charles has gone through that honeymoon period at Ferrari and now it is about knuckling down and this year has got to be the year he fights for the championship,” Button told the Daily Mail.

“There were some races where Charles was making quite a few mistakes at the start of the year.

“He had massive speed but even he said, “oh sorry guys, that was my fault”. It’s like, maybe back off saying it is your fault every time.

“But I can’t wait to be watching what unfolds at Ferrari. I really think they will pull it together and take it to Mercedes," he added.

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A big question heading into 2020, is whether the relationship between Leclerc and teammate helps or hinders Ferrari in their quest for a first championship since 2008.

Button himself has already suggested the pair will get along much better than at times towards the end of last season and believes both can focus on their shared aim.

“I think the dynamic was just wrong within the team [last year],” he said. “I think now they have a much better understanding of each other and I really feel they are going to be a strong team in 2020.

“As soon as they realise they have to be fighting Lewis [Hamilton], rather than each other, they will have a great chance of being at the front of the fight, and fighting for the championship.”

Also in focus will be the future of Vettel, who is out of contract at the end of 2020.

Already, Ferrari has suggested they are happy to keep the 32-year-old but Button believes the first run of races will be crucial t the outcome of that process.

“I can imagine, it would have been horrifically tough,” he said, reflecting on Vettel's 2019.

“Being a four-time World Champion and this young kid coming in and outscoring him and getting more pole positions than him. That’s tough, really tough, and it is how you handle that.

“I don’t think at times he handled it great but now looking back he has got the experience of working with him and everyone looks at how Charles is as good as Sebastian already so it is a little bit easier.

“Now he goes out and if he is a bit quicker then it’s 'oh, he’s a bit quicker, I’ll work here and outperform him in the next race' and I think that’s a good place to be for Sebastian. It’s a much stronger position to be in I do feel.

“When you are beaten by a young kid in your team it hurts, a lot," Button admitted. "How many hours he has put into working with Ferrari, four World Championships with Red Bull, that really does hurt.

“I think he will be a much more confident driver and will make less mistakes in 2020. If he doesn’t… he probably won’t be at Ferrari in 2021.”