Red Bull team principal Christian Horner has revealed that Sebastian Vettel considered retiring from Formula 1 last season.

The 27-year-old, who will drive for Ferrari this year, endured a torrid time as he looked to defend his world crown and became so disenchanted with things that he considered quitting the sport.

"There was probably a stage last year where he thought about whether he wanted to stop or not, whether he was getting the same level of enjoyment and whether he wanted to continue," Horner is quoted as saying by The Telegraph.

"He was just unhappy with the direction F1 had gone in. The previous four years had been so successful for him, with a car that he loved driving, then suddenly things were very different.

"It raised questions he had to deal with. He went back to basics, he drove a kart in the middle of the year, and got back to the essence of why was he a grand prix driver and rediscovered his passion for it."

Vettel ended the last campaign sitting in fifth place in the drivers' standings, failing to win a single race all term.