Helmut Marko believes Daniel Ricciardo lost his "killer instinct" in the years away from Red Bull as he explained the Australian's RB exit.
On Thursday, it was confirmed Ricciardo has been replaced at Red Bull's RB team for the remainder of 2024 by reserve driver Liam Lawson, with the New Zealander joining Yuki Tsunoda from Austin's US Grand Prix onwards.
The news all but marks the end of a 14-year stint in F1 for 35-year-old Ricciardo, who is now mulling over his future in racing.
As a Red Bull junior, Ricciardo rose through the ranks to compete for the main team between 2014 and 2018 and he became one of F1's standout performers during that era, collecting seven wins alongside Sebastian Vettel and then a rapidly emerging Max Verstappen.
Ricciardo was persuaded by Renault team boss Cyril Abiteboul to make the jump to the Enstone-based team for 2019, but struggled to repeat his Red Bull successes in uncompetitive machinery.
After two fruitless seasons Ricciardo moved to McLaren but, despite taking an eighth win at the 2021 Italian Grand Prix, he endured two frustrating seasons trying to adapt to the team's machinery, before being cut loose one year before the end of his deal in 2022.
Speaking exclusively to Autosport's German sister site Motorsport Total, Marko believes Ricciardo's career never recovered from leaving Red Bull in the first place, and says the Australian has lost his "killer instinct" along the way.
"I think the decision to leave Red Bull Racing was the turning point in his career," Marko said. "Then he didn't have a winning car at either Renault or McLaren. He did win at Monza, but those were special circumstances.
"I don't know what exactly happened, because if we knew, we would have helped him. But the speed and, above all, this late braking, and then he goes left or right... in these last few years he tried but it was no longer there, the killer instinct was gone."
Marko believes question marks over his status alongside Verstappen and the strength of Red Bull's Honda power units both played a part in Ricciardo leaving Red Bull for Renault.
"He had certain reservations about the Honda engine and apparently he listened more to the sweet talk of Renault and Cyril Abiteboul," Marko explained. "Financially, there wasn't much difference between what Renault offered him and what we offered.
"I also told him: 'Shoeys will be hard for you'. I don't think we've seen Renault on the podium a lot.
"He came to us, beating Vettel with three-to-zero victories in 2014 and after that, Daniil Kvyat was faster than him at times, but over the season he also had him under control.
"And then Max came and he got stronger and stronger, so that was certainly one of the reasons for his decision to choose Renault over us."
Amid unease among fans over how Ricciardo's exit was communicated and spilled out into the Singapore weekend, before the official announcement on Thursday, Marko says Ricciardo was informed about what would happen and felt his fastest lap was a fitting send-off.
"[The timing] was related to a variety of factors and obligations," he explained. "He was informed, and the worthy farewell performance was, I think, the fastest lap.
"That still showed what potential he has, not continuously and not at the level that would have justified him coming to Red Bull Racing, but that was an impeccable performance.
"I think it was clearly communicated that he has to be significantly better than Yuki Tsunoda and he only managed that in a few races, so it was clear that this story of the prodigal son rejoining Red Bull Racing unfortunately didn't work out.
"He said very well that he is at peace with himself, and he has come to terms with the situation and we will see what his plans for the future are."
