Australian Formula One driver Daniel Ricciardo says he wasn’t surprised at Sebastian Vettel’s decision to quit Red Bull, and believes it was triggered by a desire for a new challenge.

The Austrian team confirmed at the start of the month the man they helped win four consecutive Formula One titles would be departing at the end of the year, with Daniil Kvyat promoted to his race seat from Toro Rosso.

Later, team principal Christian Horner let the cat out of the bag by revealing Ferrari had poached the 26-year-old German.

When Ricciardo first heard the news he concedes he was far from surprised, saying: “I was pretty open to anything.

“I expected him to stay, I expected him to leave, so I wasn’t shocked when he announced he was leaving.

“The way I see it, he has won four titles with Red Bull and obviously he has an opportunity elsewhere.

“Before he sees himself getting a bit too old for the sport, he probably wants another challenge.”

The suspicion is Ricciardo has also put Vettel’s nose out of joint as the latter was understandably the dominant force in his previous relationship with former teammate Mark Webber.

But in a car not to his liking following the changes brought about by the introduction this year of the 1.6-litre V6 turbo-charged power units, Vettel has been outperformed by Ricciardo.

Other than Mercedes duo Lewis Hamilton and Nico Rosberg, Ricciardo is the only other driver to win a race this season, taking the chequered flag on three occasions.

Ricciardo insists, however, in public Vettel has accepted his fate with good grace.

“He has been fair with me from day one, and after the third win was still very fair and very respectful with me,” added Ricciardo.

“As the season goes on he would love a win, so maybe inside there is a bit more frustration. I am sure deep down he wants to get a win this year.

“When you see a teammate win races and you’re not, naturally you are frustrated, but I wouldn’t say that has been displayed in meetings or anything I have seen.

“To his credit he hasn’t taken anything out on me, or in front of the team.

“Maybe behind closed doors, but not visible to any of us, so I think he has controlled it well.”