Championship leader Sebastian Vettel has tipped his old team Red Bull to return to the top in Formula 1.

Currently, the 2017 title looks to be a fight between Ferrari - for whom former Red Bull driver Vettel now races - and Mercedes.

However, after the opening four 'flyaway' races, it is rumoured that a 'B' car in the works by Red Bull could be up to a full second per lap quicker for Barcelona.

"I think [Spain] will be a very close race between Mercedes and us, and I also hope that Red Bull find some pace," said Vettel, who won all four of his titles for the energy drink-owned team.

"There's a lot of rumours around. They are a strong team, they know how to build a quick car so I expect it's a question of when rather than if."

Red Bull are currently in third position in the standings with 57 points to second-placed Ferrari's 135.