Vettel pondered F1 exit amid career crisis - Horner

That is the claim of Christian Horner, who as Red Bull team boss witnessed first-hand the German driver's slide from four consecutive world titles to the struggles of 2014.

Last year, Vettel notably struggled to adapt to the sport's new V6-powered format, and failed to stand even once at the top of the podium while teammate Daniel Ricciardo won three Grands Prix.

Vettel was not happy

"You could tell he (Vettel) wasn't happy," Horner told reporters on Tuesday as he presented to the media Red Bull's new lineup of Ricciardo alongside Russian youngster Daniil Kvyat.

"There was that feeling 'am I (Vettel) enjoying this as much as I thought I was?'" Horner explained.

"It was like someone had taken his toy away. He went through a period of disillusionment about the direction Formula One was going in.

"There was a stage last year when he thought about whether he wanted to stop or not, whether he was getting the same level of enjoyment or not and whether or not he wanted to continue," he added.

Horner said Vettel, 27, ultimately got to grips with the 'new' F1, but also true is that the German had been in the process of deciding to switch to Ferrari for 2015.

A new challenge will be good for Vettel

"I think Sebastian felt the timing was right in his career," he said. "He needed that stimulus of a new challenge."

However, not everyone in the paddock is convinced Ferrari is the forum for Vettel to rekindle his passion, especially given the turmoil that has taken place at Maranello in the past months.

Niki Lauda, the team chairman at Mercedes, said Mercedes' current dominance was not born overnight, and "even for Ferrari it will take four years".

And if there are signs that Ferrari's revival might even take longer, "then Sebastian will start to feel the pressure, the politics, the media, which at Ferrari is twice as bad as it is at Red Bull," the F1 legend told Auto Motor und Sport.