Horner: Vettel's F1 outbursts caused by his 'killer instinct'

Vettel is locked in a tight championship battle with Hamilton, and courted controversy last month when he swerved into the Mercedes driver behind the safety car in Baku.

Ferrari driver Vettel reacted angrily over his team radio as he drove into Hamilton, suggesting he had been brake tested at the previous corner, but later accepted at an FIA hearing he was in the wrong.

He also ranted at race director Charlie Whiting at the Mexican Grand Prix last year after finding out Max Verstappen has not been awarded a penalty for cutting the first corner.

Horner, who was Vettel's team boss at Red Bull for six seasons, said the German's actions are a consequence of his fierce competitive streak.

"Sebastian wears his heart on his sleeve and is involved in a very intense battle," said Horner.

"He sees an opportunity to be a champion again this year and he knows he's going to need everything going his way against Mercedes to achieve that.

"He has zero filter between what he thinks and what he says sometimes or what he does and that's the great side of him.

"But sometimes it gets him in hot water as well."

Horner said Vettel shared character traits with seven-time champion Michael Schumacher.

"Sebastian is a great character," he said.

"You don't see much of that in his current environment.

"He's a fun guy, he loves British humour, he's very good with the mechanics of teams.

"He was always very generous not in just gifting something to the team but also for the whole factory.

"He's got this huge desire, the records mean a lot to him.

"Michael Schumacher was very much his idol and I think what we see sometimes is that killer instinct of 'I want to win', sometimes at all costs."

LEAVING FERRARI WOULD BE 'JOB HALF DONE'

Vettel does not have a contract with Ferrari beyond the end of 2017, but although Horner suspects Mercedes are talking to Vettel he would be surprised if he moved.

"I'd be amazed if he left," said Horner.

"I would think he's got Toto in his ear trying to say extend for a year and then he's probably got Ferrari saying it's three years or nothing.

"I guess he wants to see through what he started at Ferrari.

"He went there for a reason, to build something and very much emulate what Michael had done.

"Stepping out now with the progress they have would be a job half done."