Red Bull principal Christian Horner has suggested that the team's 2015 campaign is "pretty much a write-off" after a poor start to the season.

The four-time constructors' champions were well off the pace of the leading pack at the Spanish Grand Prix, with Daniel Ricciardo finishing seventh and teammate Daniil Kvyat coming home in 10th in Barcelona.

While neither car suffered from the engine reliability issues that has blighted the team this season, Horner claimed that the Renault power unit is still lacking in pace.

He told reporters: "I think we are so far on the back foot with reliability.

"To be honest with you, this year is pretty much of a write-off. You have just got to go for it - even if you end up using 20 engines.

"It would be better to learn and make progress in preparation for next year than be conservative. It is far easier to make a fast engine reliable than a reliable car fast. Our philosophy has always been to push performance."

Volkswagen have recently been linked with a move into Formula 1 as Red Bull's engine partner.