Christian Horner has revealed that Red Bull's motorsport adviser Helmut Marko wanted Daniel Ricciardo out of the RB team as early as this year's Spanish Grand Prix in June.
Confirmation that the eight-time race winner would be replaced by Liam Lawson at Red Bull's junior team was announced last week after the Singapore Grand Prix, meaning Ricciardo's 257-race career is likely at an end.
The 35-year-old Australian returned to RB midway through last year with the aim of impressing Red Bull's management enough to be considered as a potential replacement for Sergio Pérez at the senior team.
However, with Lawson on the sideline as a reserve driver, Horner said Ricciardo's own position was at risk after just 10 races as he struggled to match the performance of RB teammate Yuki Tsunoda week-in and week-out.
"I think it was the lack of consistency," Horner told the "F1 Nation" podcast.
"I mean he started the season roughly, then Miami was a weekend of two halves, the Friday and Saturday morning was fantastic and it looked like the Daniel of old, defending against Ferraris, out-driving the car, but then Saturday afternoon and the Sunday were disastrous.
"Even around Barcelona, Helmut wanted him out of the car, there was already a lot of pressure on him there."
Marko, who remains an influential figure within Red Bull's motorsport activities, has spoken on numerous occasions this year about the importance of Lawson returning to the fold.
Horner said he worked hard to give Ricciardo as many opportunities as possible to retain his position, but there was never a convincing enough argument that he would fulfil his target of being a genuine candidate to replace Perez.
"I've done my very best to buy him as much time in the car to allow him to deliver, so otherwise he would have been out of the car after Barcelona," he added.
"All the drivers are under pressure to deliver but the reason that Daniel was in that car was to get himself back into a position to ultimately be there to pick up the pieces if Checo [Pérez] didn't deliver.
"And the problem was they both had issues with form at varying times, Checo started the season very well, very strongly and Daniel was struggling, and then as Checo lost form Daniel found a bit of form but it was never compelling enough to say OK we should switch the two drivers."
The Red Bull team principal said Ricciardo has been offered an ambassadorial role with the brand, but admitted the chances of another return to racing were slim.
"Daniel is just a brilliant character, a brilliant human being -- he lights up a room when he walks into it," Horner added. "I hope he stays around the sport.
"We've made it very clear that we want him to remain in an ambassadorial capacity with the team, and of course one never really knows. I mean, if Liam doesn't get the job done, if Checo doesn't get the job done, we know what Daniel's capability is.
"But I think for him, he knows, at the age that he's at, he's had a great career. So many memories.
"The most disgusting thing ever was drinking champagne out of his sweaty boot [as [part of Ricciardo's race-winning celebrations]! But he made it his own and he got some incredible people to drink the champagne from his sweaty shoe."