Red Bull team principal Christian Horner believes Daniel Ricciardo opted to leave for Renault as he was concerned that he would be deployed in a support role to Max Verstappen. Ricciardo reneged on a one-year agreement with Red Bull last week to pen a two-year agreement with the French squad.
The Australian had even recorded a video message to announce a new deal with Red Bull, but pulled out at the last minute.
Swapping a team that has helped him to seven grand prix victories for one that has not secured a podium since 2011 is clearly a risk but Horner talked up Ricciardo wanting to "have a leading role, perhaps in a smaller environment".
"Daniel said he decided after a long flight to America that he wanted a change," said Horner on F1's official podcast 'Beyond the Grid'.
"If you look at the rational reasons for that, it's difficult to understand.
"Daniel had his reasons. I think it comes back to wanting to take on, 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 better words.
"It's not that they were treated in any way different. They would have absolute equal status, as they've always had. I can't help but feel that was perhaps a large part of Daniel's decision.
"The competition between him and Max is intense. I think Daniel's just decided the timing is right for him to check out and try something else."
Horner claimed that moving to Renault represents a "massive risk" for Ricciardo, who previously stated his intention was to start 2019 in a certified race-winning car.
"I thought he was winding me up to be honest when he rang me to say 'I'm going to Renault'," Horner added. "I said, 'is this a wind-up for the summer holidays'?
"It then became very clear that was his choice and you have to respect that.
"Renault is a growing team, they are committing resource there. Maybe it's an inspired choice."