Defending drivers world champion Sebastian Vettel said he still feels ‘vulnerable’ despite winning the past four races to open up a 13-points lead in this year’s title race.

Speaking ahead of this weekend’s Abu Dhabi Grand Prix, the 25-year-old German said he and the Red Bull team could easily suffer setbacks to upset their current domination.

He said: “If you just look back, India was a great race for us but a couple of laps from the end we had some sparks.

“Obviously it was not a problem, but it doesn’t take much imagination (to see that it could have been).”

Vettel also does not believe Red Bull has proved to be the fastest car despite his string of wins.

“I think in the second stint on hard tyres (in India), McLaren and Ferrari were arguably a little bit quicker than us. But then I could benefit from the gap I had after the first stint.”

Title rival Fernando Alonso agreed mechanical reliability could be a key focus for both teams in the final three races.

Speaking to reporters at the Yas Marina Circuit, he said Ferrari would try to be ‘bullet proof’ and test the fragility of the Red Bull team.

“Mechanical failures are always in the air. It is not only for them, it is for all of us,” Alonso said.

“If we do (have problems) it will be very difficult to fight for the championship.

“We know that Red Bull sometimes is a little bit more fragile. We saw in the last race that Mark Webber lost his KERS (Kinetic Energy Regeneration System).”

Red Bull could secure the constructors’ championship in Abu Dhabi this weekend – something Vettel said he was unaware of until informed by Australian teammate Webber.

“We were on the same plane and Mark said it would be quite bad for the constructors’ if this plane went down…” Vettel joked.

“Obviously it would be very special for us to win the championship here, but in order to do so we have to have a strong weekend and score more points than the others.”

Red Bull are 91 points ahead of Ferrari and 101 ahead of McLaren.