Red Bull team boss Christian Horner believes the idea of playing a “support role” to team-mate Max Verstappen was a key factor in Daniel Ricciardo’s decision to join Renault for 2019.

The Australian recently shocked the paddock with his decision to end his 10-year association with Red Bull to sign for the Enstone-based outfit on a two-year deal.

Ricciardo was promoted to the senior team in 2014 to replace countryman Mark Webber, and in that time has claimed seven grand prix victories – including this year’s Chinese and Monaco Grand Prix’s.

Speaking for the first time since Ricciardo’s announcement, Horner said he respected his decision but feels he’s taking an “enormous risk” at this phase of his F1 career.

“I thought he was winding me up to be honest with you,” Horner told the official Formula 1 podcast. “He rang me to say I’m going to Renault. I said: ‘You what? Is this a wind-up for the summer holidays?’

“But it then became very clear that was his choice and you have to respect that. Renault are a growing team, they’re committing resource there.

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“I think it comes back to wanting to take on, in his words, a new challenge but I also feel he sees Max growing and growing in terms of speed and strength and he doesn’t want to play a support role I guess, for want of a better word, not that they are treated in any way differently.

“They would have equal status, as they have always had. I could understand if it was to Ferrari or Mercedes, but it’s an enormous risk at this stage of his career.”

With Ricciardo departing next season, Red Bull has an unexpected vacancy to fill alongside Verstappen, with Carlos Sainz and Pierre Gasly the early favourites to take the seat.

Fernando Alonso, who’s yet to decide his immediate future, has also been linked with a switch to the Austrian outfit. However, Horner played down the prospect of the double world champion joining the team, suggesting Alonso is prone to causing “a bit of chaos” wherever he goes.

“I have got huge respect for Fernando. He’s a great driver, a fantastic driver,” Horner added.

“But I think it’s very difficult to see… he tends to cause a bit of chaos wherever he’s gone. I’m not sure it would be the healthiest thing for the team for Fernando to join the team.”